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Cows with better versus poorer lifetime calf production did not differ significantly in intake or passage rate of digesta under ad libitum concentrate or roughage feeding. On the concentrate diet, better cows tended towards greater fat accretion than poorer cows. On roughage they maintained, while poorer cows lost fat thickness. Key words: Cows, intake, passage rate, fat thickness

The effects of time on feed and of ambient temperature on water intake, and the effects of preconditioning and shearing treatments and of ambient temperature on body temperature and respiration rate of feedlot lambs were examined. Daily ambient temperature maximum, minimum and range averaged 27.5, 10.8 and 16.7 C, respectively, for 56 days between July and September. For the first 24 days that the lambs were on feed, water intake was not affected by ambient temperature. Intake did increase linearly with day (b = 160 ml), concurrently with increasing feed intake. During the remaining 32 days, water intake per lamb increased 139 ml per 1 C rise in average daily ambient temperature. Afternoon body temperature, morning to afternoon body temperature change, and respiration rate all increased with increasing ambient temperature. Preconditioning 1 wk before weaning (pneumonia, ovine ecthyma and enterotoxemia vaccinations and drenching for tapeworms, intestinal roundworms and coccidia) vs. conditioning the lambs with the same treatments at the time of weaning and shipment did not affect body temperature or respiration rate. Lambs sheared with a clipper attachment which left a 1-cm fleece stubble averaged 0.3 C lower in afternoon body temperature than either close-shorn or unshorn lambs.

Two hundred twenty-five lactation and litter performance records from 82 does representing four genetic groups and two diets were analyzed to quantify breed, heterosis, reciprocal F1 cross and diet effects for milk production and associative traits. Doe genetic groups were New Zealand White (NN) and Californian (CC) straightbred and Californian X New Zealand White (CN) and New Zealand White X Californian (NC) reciprocal crossbreds. Pelleted diets fed to does and litters were either a commercial control or a 74% alfalfa diet. Three sire breeds of litters included NN, CC and Flemish Giant (FG) straightbreds. Doe genetic group and diet were important sources of variation (P less than .05) for all traits examined except for litter milk efficiency (litter gain/milk intake) and doe feed efficiency (milk yield/feed intake). The sire breed of litter effect did not influence (P greater than .05) lactational performance of does nor associative preweaning traits. Straightbred NN does were heavier at kindling, yielded more milk, reared a heavier litter by 21 d and were more efficient in converting feed into milk than were straightbred CC does (P less than .01). Significant heterosis was detected for milk production and for litter size and weight at 21 d. Reciprocal differences between crossbred doe groups were observed (P less than .05) for litter milk efficiency and doe feed intake. The 74% alfalfa diet was superior to the commercial control diet for effects on milk production and litter size and weight at 21 d, although doe feed intake was increased.(ABSTRACT TRUNCATED AT 250 WORDS)

Summary Relationships among hemoglobin (Hb) types and production traits were examined in 294 crossbred ewes from North Country Cheviot, Dorset, Finnsheep and Romney rams, and Suffolk and Columbia-type ewes. Hb BB ewe lambs were youngest at first estrus, while Hb AA ewe lambs were oldest. Ewe lamb fertility was similar for Hb AB and Hb BB ewes, and both were superior to Hb AA ewes. When Finnsheep crossbreds were excluded, frown which Hb BB was absent, Hb BB ewes had higher ewe lamb fertility than did Hb AB ewes. There was a minor advantage of the A over the B allele in ewe lamb prolificacy. Hb BB ewes were highest, Hb AB ewes were intermediate and Hb AA ewes were lowest for average fertility, prolificacy per ewe lambing, lambs born per ewe exposed to mating, total number of lambs weaned and total kilograms of lamb weaned. Grease wool production, staple length, fiber diameter grade, incidence of medullated fibers and incidence of cotted fleeces all were similar across Hb types. Likewise, Hb type did not affect milk production or composition. Ewes with Hb AB had the lowest incidence of footrot; Hb AA and Hb BB ewes were similar. Ewes with Hb AA had the lowest fecal parasite egg counts, while ewes with Hb AB or Hb BB were similar. Ewes with Hb AA also had the lowest incidence of mastitis, Hb BB ewes were intermediate and Hb AB ewes were highest. The combination of overdominance (as for footrot resistance), beneficial effects of the A allele on health-related traits (as for mastitis and parasite resistance) and the beneficial effect of the B allele on reproductive traits, if real, could partly explain the genetic polymorphism commonly reported at the Hb locus in sheep.

This study was designed to determine whether periodic exposure to pre-recorded sound associated with feed delivery and consumption would alter feed intake or feeding pattern of lambs provided with fresh feed once daily. Thirty cross-bred lambs were randomly assigned to 6 pens. The trial lasted 44 days (30 July to 11 September 1982) and consisted of a 4-day acclimation to test facilities, and then cycles of 4 days without sound stimulation followed by 4 days with sound stimulation. Sound stimulation consisted of 6-min broadcasts, every 3 h, of sounds associated with feed delivery and eating. Lambs were observed continuously for 24 h on 3 days when lambs were subjected to sound stimulation and 3 days when they were not. The recorded sound stimulation affected neither feed intake nor feeding behavior. Lambs largely ignored the recorded sounds, and total feed intakes during 20 sound-stimulated vs. 20 non-sound-stimulated days were 1234 vs. 1240 kg, respectively. There was a rhythmic feeding pattern at 1–2-h intervals, synchronously throughout the barn, and this was not affected by the 6 min of sound stimulation at 3-h intervals. There were no major peaks in feeding activity except after the offering of fresh feed in the morning. Feeding activity did not change with sunrise or sunset, and peaks of eating activity were distributed at even time-intervals throughout the 24 h. The overall means per lamb for the total time spent eating, the number of eating bouts (separate eating incidents), the average time eating per bout and the number of drinking episodes across the 6 observation days were 118.8 min, 22.6 times, 5.5 min and 9.6 times, respectively.

Twenty-eight cows were assigned randomly to a daily photoperiod of 18 h light and 6 h darkness or to continuous light and were observed 1 day each month from December 1981 to February 1982. Lighting regimen did not affect eating behavior or milk production. Overall means of total eating time, number of eating bouts, and average time eating per bout on the 3 observation days were 270 to 280 min, 10 to 12 times, and 24 to 27 min. Eating behavior and milk production were not significantly correlated. Eating patterns were similar in both groups and across observation days. Peaks of eating activity occurred before sunset, bracketing the evening milking and after the offering of fresh feed in the morning. Approximately 80% of total eating activity occurred between 0900 and 2100 h in both groups. Cows had a clear preference for entry into the right or left side of the milking parlor, and entry order was repeatable. Milking order and milk production were not correlated. In one group, location of free stalls did not influence utilization; but in the other group, centrally located stalls were utilized more than stalls at either end of the alley. About 40% of cows had individual free stall preferences.

Each of 9 beef × dairy crossbred cows was presented with 2 alien calves within 5 minutes of parturition. Each cow's own calf was removed and later fostered to another cow. Foster trios were observed periodically until introduction to the foster herd. The foster herd was observed continuously on Days 71, 77 and 175 after the average fostering date. Calf growth rates were recorded from birth to Day 77 and from Day 77 to Day 175. All cows were observed to allow their foster calves to nurse at the time the trio was introduced to the herd, suggesting that successful maternal-offspring bonding between calves and dam had occurred. Behavioral data taken on Days 71 and 77 were similar and were summed. Percent cross-suckling was high on Days 71 and 77 but was less on Day 175. Calf growth rates were highly variable to Day 77, and were less variable between Days 77 and 175. A high negative correlation existed between percent cross-suckling and calf growth rate to Day 77. The decrease in percent cross-suckling from Day 77 to Day 175 was directly proportional to an observed decrease in suckling frequency. Percent cross-suckling was highly variable among calves during all observation periods. The negative relationship between percent cross-suckling and calf growth rate was less evident at Day 175, possibly due to increased consumption of forage and creep feed by calves at that time. Variation among foster pairs for growth rate was not significant. In many cases, the fostering methods employed apparently did not result in the formation of a specific maternal bond between the cow and her foster calves.

Behavior of sheep isolated in a 6 m diameter enclosure, then exposed to a tethered dog in the same setting, was examined. Subjects were 2 and 3 year old crossbred ewes (North Country Cheviot, Dorset, Finnsheep, and Romney sire × Suffolk and Columbia-type dam matings). Each of 164 ewes was tested three times with 3 weeks between tests. Ewes were scored for ambulation (number of steps taken) when isolated for a 90 s period and when exposed to the dog for an additional 90 s period. Subjective investigation score, subjective emotional behavior score, number of vocalizations, number of foot-stampings, and number of eliminations (urinations plus defecations) were also examined. These traits were chosen because published research with farm mammals and rodents has indicated they are related to emotional behavior or nervousness. Ewes typically responded to isolation by initial high levels of ambulation which decreased to immobility by the end of the first 90 s. Vocalization occurred in 73% of the observations but foot-stamping occurred very rarely in the first 90 s of observations. Upon exposure of the dog, ewes commonly took several steps, then became and remained immobile for the duration of that 90 s observation. Vocalization was rarer but foot-stamping was much more common than during the period in which ewes were isolated. Eliminative behavior occurred in 53% of the observation periods and was not affected by exposure to the dog. In this experiment, high ambulation during isolation was related to greater emotional behavior, while immobility during exposure of the dog was related to greater nervousness. Vocalization and foot-stamping were predictable responses to isolation and dog exposure, respectively, but both occurred with too low a frequency to be useful measures of variation in emotional behavior. Differences between ewes with Suffolk vs. Columbia-type inheritance were small and not consistent. Ewes with Romney sires had higher scores for ambulation, investigation score, emotion score and vocalization, and ewes with Finnsheep sires scored above average for vocalization and eliminative behavior. Dorset and North Country Cheviot sired ewes were average or below for most of the traits assessing emotional behavior.

Reproductive characters (N = 430 matings) of four doe genetic groups and preweaning performance of litters (N = 280) were evaluated in a 15-mo study. Doe genetic groups were New Zealand White (NN) and Californian (CC) straightbreds and Californian X New Zealand White (CN) and New Zealand White X Californian (NC) crossbreds. Does and litters were provided either a commercial control or a 74% alfalfa pelleted diet. Sires of litters included NN, CC and Flemish Giant (FG) straightbred bucks. The linear and quadratic regression on age of dam affected (P less than .01) litter birth weight. The NN does were heavier than CC does at first breeding at 154 d and produced heavier litters at birth and weaning (all P less than .01). Percentage survival of kits from birth to weaning and doe and preweaning litter feed intake and efficiency were greater from NN than CC does (all P less than .01). Numbers born and reared/litter to weaning at 28 d were likewise greater for NN vs CC straightbred does. Heterosis estimated from comparing litters of reciprocal crossbred vs straightbred does was significant for number born, litter birth and weaning weights and doe and preweaning litter feed intake. Reciprocal crossbred differences were observed (P less than .05) for doe breeding weight, number born and weaned per litter, litter birth and weaning weights and doe and preweaning litter feed intake, favoring CN does reared by NN straightbred dams over NC does. Diet, in consistent favor of the 74% alfalfa diet, significantly affected all traits studied with the exception of doe longevity, doe fertility percentage, and doe and litter feed efficiency.(ABSTRACT TRUNCATED AT 250 WORDS)

Statistical properties, inheritance of spermatozoan midpiece length, and its association with bull reproductive traits and daughters' dairy traits were examined in a sample of 39 Holstein bulls. Variation for midpiece length of individual cells was small within bulls (coefficient of variation ⋍ 4.5%), but midpiece length did vary among bulls. Average midpiece length did not differ in ampules of semen collected from the same ejaculate but did differ between ampules of semen from the same bull collected at least 6 mo apart. Two methods of estimation yielded heritabilities of midpiece length greater than one. Both were imprecise but consistent with additive genetic variation for the trait. Moderate correlations between a sire's midpiece length and his Predicted Difference for dairy production traits were negative. Correlations between midpiece length and semen quality and fertility were close to zero. Results suggest that midpiece length is heritable and that it might be correlated with economically important dairy production traits.

The regression of prolificacy on duration of estrus was positive in 18-mo and positive after 18 h in 30-mo-old ewes. Ewes bearing twins were in estrus longer than ewes bearing singles. The relationship was not strong enough, however, to allow accurate prediction of prolificacy from estrous duration.

Methods for calculating the probability of detecting a carrier of a recessive gene by utilizing matings among related individuals are presented for single and litter bearing species. The confidence level for detection of heterozygosity depends upon: (1) the genetic relationship between mates, (2) the number of mates per male and the number of offspring per mate, (3) whether an estimate of recessive gene frequency before selection is available and (4) the magnitude of that frequency. Methods of computing probability of heterozygosity vs homozygosity utilizing Bayes theorem also are presented. In the conventional progeny test method, a sire initially is assumed heterozygous before calculations are made, but no prior information concerning his probable genotype is utilized. In the method using Bayes theorem, prior sources of information from relatives or from estimates of population allele frequency are utilized. This method gives the exact probability that a sire is not a carrier, given prior information and that he produces all normal offspring. These methods could be used in any sexually reproducing species to identify not only detrimental genes but beneficial genes as well.

Six hundred sixteen ewes of six strains were inoculated twice with ovalbumin in Freunds' incomplete adjuvant. To quantify the humoral immune response to the foreign antigen, blood samples were collected from all ewes 1 wk post-second injection. Blood samples were also collected between 4 and 40 h of age from their 709 lambs, to examine genetic differences in ability of lambs to acquire maternal anti-ovalbumin antibodies. Titers of anti-ovalbumin antibodies were determined using kinetic enzyme-linked immunosorbent assay (ELISA) techniques. Strain did not affect ewe immune response, but sire within strain was highly significant. In pregnant ewes, anti-ovalbumin antibody titers in 12- and 30-mo-old ewes were higher than those in 21-mo-old ewes. Number of lambs in utero did not significantly affect ewe immune response. Heritabilities of anti-ovalbumin titer from a paternal half-sib analysis were .27 +/- .17 for all ewes and .57 +/- .25 for only the pregnant ewes. The effect of strain of lamb on lamb anti-ovalbumin titer approached significance, and sire within strain was highly significant. Lamb anti-ovalbumin antibody concentration increased as time from birth to blood sampling increased to 18 h but declined thereafter. The size of the litter in which a lamb was born had a highly significant effect on the lamb's acquired immunity, with titer decreasing as litter size increased. The heritability estimate for lamb anti-ovalbumin antibody concentration from a paternal half-sib analysis was .38 +/- .11; it was .28 +/- .15 from the sire variance component of a full-sib analysis. When lamb titer was considered a maternal trait (lambs nested within their maternal grandsires within strains), the maternal grandsire variance component was negative. The average anti-ovalbumin antibody concentration of lambs that died between blood sample collection and 120 d of age was less than the average antibody concentration of lambs that survived (P less than .01).

The effects of sire breed, dam genetic group and diet on postweaning litter growth and mortality were evaluated in 208 litters of rabbits. Sire breeds were New Zealand White (NN), California (CC) and Flemish Giant (FG). Dam genetic groups were NN and CC straightbred and California X New Zealand White (CN) and New Zealand White X Californian (NC) reciprocal crossbreds. Litters were fed either a commercial diet or a 74% alfalfa diet. Litter size and weight at 56 d and litter gain (the difference between 56- and 28-d litter weights) tended to be lower in NN- compared with CC-sired litters; while feed intake was significantly lower and mortality was higher in progeny of NN sires. Litter 56-d weight, litter gain and litter feed efficiency (gain/feed intake) were improved (P less than .05) in litters sired by FG vs NN or CC bucks. Direct heterosis (CN and NC compared with NN and CC litters) for litter size, growth and feed-related traits was generally low (less than 11% in absolute value), while moderate heterosis levels (-21 and -22%) were observed for diarrhea-related and total mortality. Differences between NN and CC straightbred dams for litter size and weight at 56 d and litter gain were small, but in favor of NN dams. Diarrhea-related and total mortality were higher (P less than .05) in litters reared by NN vs CC straightbred dams.(ABSTRACT TRUNCATED AT 250 WORDS)

Verifications and validations were conducted of a simulation model of beef cattle production on tropical ranges of the Colombian Llanos. Liveweight changes were simulated for individual cows sampled at random, for cow herds alternately grazing native savanna and molasses grass (Melinis minutiflora) and for steers grazing native savanna. Correlation coefficients between observed and simulated liveweight change were high. Simulations of the calving rates of cow herds from two experiments at Carimagua Research Station were also conducted and there was reasonably good agreement between observed and simulated data. Shortcomings of the model included an inability to simulate the heavy weight losses of grazing animals on molasses grass during the dry season and under-estimates of calving rates for the most productive herds. An experiment was conducted with the validated model from which it was concluded that grazing molasses grass and weaning of calves at 84 days of age would do little to increase calving rate.

Fifty-six feeder lambs were observed each half-hour for one day per week for 7 consecutive weeks between July and September, 1973. At each observation period, the number of lambs eating, drinking, standing in an alert state, lying down and standing inactive was counted. The average number of lambs engaged in each activity over the 7 days of observation was plotted against time. Two peaks of eating, drinking and standing active occurred near sunrise and sunset. During the eating peaks, there was frequently competition for space at the self-feeder. At mid-day, lambs were inactive, standing about in groups, shading their heads under the flanks or between the hind legs of adjacent lambs. Later in the afternoon, lambs utilized the shade that became available from the perimeter fence. In both cooling strategies, lambs were particularly keen to shade their heads. All activity declined after sunset, and throughout the hours of darkness the majority of the lambs were lying down.

A simulation model was developed to study voluntary forage intake, energy requirements for maintenance, liveweight change and calving rate of grade Zebu cows in the Llanos of Colombia. Multiplicative correction factors were fitted to intake and maintenance requirement prediction equations researched from the literature to account for reduced intake due to sparse regrowth of recently burned native savanna and to conditions of mineral deficiency, increased intake and decreased maintenance requirement during periods of high compensatory gain during the rainy season, and increased intake and maintenance requirement due to the effects of lactation and gestation. A frequency distribution was constructed relating liveweight at time of mating to subsequent calving rate, and this was used to simulate the calving rates of cow herds in the Llanos. Use of the model would allow prediction of the amount of improved pasture or supplemental feed that would be necessary to raise calving rates in a particular herd to an acceptable level, defined as at least three calves per cow every four years. The model was fitted by computer and was then run on programmable calculators. This type of simulation is suited to regions of the world in which computer time is expensive or unavailable. Verifications, validations and experimentation with the model are presented in a companion paper.

AbstrtactFlemish Giant (FG) and New Zealand White (NZW) purebreds and terminal crossbreds (TX) (Flemish Giant sires × Florida White-New Zealand White dams) were evaluated during a 10-month period for maternal and litter pre-weaning and post-weaning performance. For the doe traits studied, teat number was greatest and litter interval was shortest, while body weight at breeding age (154 days), litter weight at 21 days and day 1 to 21 food intake were lowest for crossbred does. These traits were similar for pure doe groups, with the exception of body weight, for which FG does were heavier. For the preweaning litter traits examined (no. = 101 litters), litter size born was smallest in the TX group (the purebred groups being similar) and was largest at weaning (28 days) for NZW. Proportion of kits born alive was lowest in FG litters, while the NZW and TX groups were comparable. Litter and average birth and weaning weights, litter daily gain, and doe and litter food intake (1 to 28 days) were all highest in FG litters and lowest in TX litters. Repeatability estimates (t) were low (t < 0·05) for litter size and birth weight traits, and were moderate to high (0·18 < t < 0·58) for the remaining maternally influenced characters. For the post-weaning litter traits studied (no. = 86 litters), NZW litters were larger in number and heavier at market age (56 days), and consumed more food from 28 to 56 days than FG and TX litters. Purebred FG litters, however, had heavier average market weights per rabbit, while purebred NZW and TX litters were similar. Mortality due to respiratory disease was higher in FG litters than in NZW and TX litters. Total mortality incidence was lowest in the TX group.

Ewes of eight crossbred groups, born in 1973 and 1974, were maintained under two pasture management systems for five and four production years, respectively. After that experiment terminated, those crossbred ewes produced Polypay-sired lambs in 1979 and were then sold. Ewe lambs from those three-bred crosses were backcrossed to Polypay rams to produce lambs from 1980 to 1983. Five ancestor-descendant data sets (three involving dams and daughters and two involving granddams and granddaughters) were examined to study relationships between production efficiency of ancestor ewes and similar traits measured on their descendants. Ancestor cumulative prolificacy was positively but not significantly associated with cumulative prolificacy in the descendants. Regressions of descendant net revenue on ancestor net revenue were predominantly negative but generally were not significant. There was a tendency for prolific ancestors to produce costly but less profitable descendants. These results may be due to economic conditions (high feed costs and low lamb values) that persisted during the course of the experiment.

Production records of crossbred ewes, including weight at mating (WTM), fertility (FRT), number of lambs born per ewe lambing (BRN), number of lambs weaned (WEN), litter weight in April (WTA) and litter weight at weaning (WTW), were analyzed for the estimation of breed differences, genotype x environment interactions and repeatability and heritability of ewe production. All ewes were from Suffolk- or Columbia-type dams. Breed of sire of ewe was Finnsheep, Dorset, North Country Cheviot or Romney, Suffolk-cross (SX) ewes were heavier at mating than Columbia-cross (CX) ewes. Cheviot-cross (NX) and Finnsheep-cross (FX) ewes were the most fertile on hill pastures, while Dorset-cross (DX) ewes were the most fertile on irrigated pastures. The FX ewes had larger litters at birth and at weaning. Columbia-cross ewes had larger litters than SX ewes on hill pastures, but the SX ewes had larger litters than CX ewes on irrigated pastures. Finnsheep-cross ewes on both types of pastures and DX ewes on irrigated pastures had heavier litter weights than NX or Romney-cross ewes at weaning. Repeatability estimates for WTM, FRT, BRN, WEN, WTA and WTW were .61, .15, .19, .08, .07 and .09, respectively. Heritabilities, from the sire-of-ewe component, were .40, .02, .12, .0, -.02 and -.05 for WTM, FRT, BRN, WEN, WTA and WTW, respectively.

For 17 days, 30 non-pregnant, non-lactating crossbred ewes, six per sire-breed (Suffolk, Clun Forest, Dorset, Polypay and Border Leicester), were grazed together during daylight hours (approximately 06.00–21.00 h Pacific daylight time) in a 0.87-ha grass—clover pasture. For the remainder of each day, the ewes were penned indoors without access to feed and water. On 6 days they were observed throughout the grazing period, with individual locations and activities being recorded every 10 min. The daily grazing pattern consisted of intensive a.m. grazing until about 10.00 h and intensive p.m. grazing after about 16.00 h. Cool, cloudy days had less distinct grazing periods than warm, sunny days. Average time spent grazing was 9.23 h (4.11 h a.m. and 5.12 h p.m.), and the average times of a.m. stop and p.m. start were 10.23 and 14.59 h, respectively. Average distance traveled was 1.39 km (0.76 km a.m. and 0.63 km p.m.). Sire-breed had no effect on either grazing time or distance traveled. Weather had a greater apparent effect than forage availability on grazing time, but forage availability had a greater apparent effect than weather on distance traveled. Sire-breed groups (averaged over observation days) differed in their grazing-site preference. A ewe's a.m. and p.m. grazing times were not correlated, but time of a.m. stop and p.m. start were negatively correlated. Grazing time and distance traveled were only moderately correlated.

Reports are reviewed in which genetic differences for sex ratio of offspring were found among breeds, breed crosses, strains, lines, line crosses, families or individuals. Although reports in which genetic variation could not be identified outnumber those in which it could, important genetic variation does exist in at least some populations. The direct or correlated response of sex ratio to selection is reviewed. Again, results are equivocal, but there is ample evidence that sex ratio will respond to selection in at least some populations of laboratory organisms. Segregation distortion in the mouse and in Drosophila is examined. Segregation distortion occurs when a heterozygous male mated to a homozygous female does not produce the two offspring types in equal proportions and the disparity cannot be accounted for by sampling or differential mortality. Although the most well-known systems have no effect (in the mouse) or only a moderate effect (in Drosophila) on sex ratio, systems in which sex ratio is subject to segregation distortion are known to exist in insects and could exist in mammals. Finally, the possibility is discussed that XX/XY chromosome chimaeric bulls, born co-twin to a heifer, might produce a preponderance of heifer progeny. A few reports suggest this might be the case, but other research is not in agreement.

The effects of twin-foster calf rearing on calf weight at 200, 291 and 365 days postcalving, on calf weight produced per cow, and on reproductive performance of cows were evaluated using fall-born calves. Eleven Holstein × Angus or Holstein × Hereford 2- or 3-yr-old cows rearing 20 Holstein or Limousin crossbred calves were compared with cows of similar age and breeding rearing 13 single-suckled Limousin crossbred calves. Twin calves were significantly lighter than single calves, but calf production per cow at 200 days postcalving was increased 39% by twin fostering. At 291 and 365 days postcalving, production per cow from twin fostering was 50% and 55% greater than that from single-suckled cows whose calves were weaned at 291 days. Twin fostering did not depress reproductive performance of the cows. However, supplemental feed costs and labor required at fostering were considered to restrict applicability of this management practice. Weaning at 9 mo as opposed to 200 days of age increased calf production per single-suckled cow without a substantial increase in costs. Key words: Cow-calf, twin foster, single-suckled, fall calving

Blood samples obtained 24 and 36 hr postparturition from 187 calves in 2 years were analyzed for serum concentration of immunoglobulins G1 (IgG1) and M (IgM). Serum and colostrum samples also were obtained from their dams, and corresponding immunoglobulin levels were determined. Calves were evaluated for their ability to acquire and absorb immunoglobulins and cows for their ability to produce immunoglobulins. Mathematical models included sources of variation for breed of sire, sire within breed, breed of dam, age of dam and sex of calf. Of these factors, breed of sire, breed of dam and age of dam were the most important. Simmental- and Pinzgauer-sired calves tended (p = .07) to have lower IgG1 and IgM levels than calves sired by Hereford, Hereford X Angus and Tarentaise bulls. Calves of Hereford X Angus dams had consistently higher immunoglobulin concentrations than calves of Hereford dams. Hereford X Angus cows tended to have higher colostrum concentrations and lower serum concentrations of the two immunoglobulins than Hereford cows. A fetal sire effect was demonstrated for serum IgM concentrations in that cows mated to Simmental bulls had lower (P = .05) concentrations than cows mated to bulls of other breeds. Advancing age of dam was associated with higher concentrations of immunoglobulins, except for serum IgM in the calf and in the cow. Correlations between serum and colostrum concentrations of both immunoglobulins in the dam were low, as were correlations between cow colostrum concentration and calf serum concentration of IgG1. IgM in the colostrum was positively associated with IgM in calf serum, however. Heritability estimates for calf serum IgG1 concentration were high (.52 +/- .28 and .69 +/- 30 at 24 and 36 hr, respectively), while estimates for heritability of IgM concentrations were intermediate (.30 +/- .26 and .35 +/- .26 at 24 and 36 hr, respectively). There was no evidence that sires within breeds influenced, through the fetus, immunoglobulin concentrations in serum or colostrum of their mates. Relatively high repeatabilities for all traits imply that observed differences among cows were due in part to genetic and (or) permanent environmental differences.

A total of 399 crossbred ewes born in 2 yr were maintained either on irrigated or dryland hill pastures. The ewes were sired by North Country Cheviot, Dorset, Finnsheep or Romney rams mated to Suffolk or Columbia-type ewes. The crossbred ewes were mated to Hampshire rams throughout the study and had the opportunity for either 4 or 5 yr of production. Annual feed cost was calculated based upon estimated annual metabolizable energy (ME) requirements for maintenance, ewe growth, pregnancy and lactation. Income from weaned feeder lambs and from orphan lambs sold shortly after birth, feed cost and net revenue were analyzed during each ewe's first production year, as well as for the entire period of the experiment. Crossbred group significantly affected income from lambs produced, feed cost and net revenue for the ewes' first production year. Crossbred group and crossbred group X management system interactions generally influenced lifetime income from lambs produced and from orphans sold, gross income, total cost and net revenue per ewe. Finnsheep X Suffolk ewes performed best on irrigated pastures but were below average for lifetime net revenue on hill pastures. Finnsheep X Columbia ewes performed best on hill pastures and, with Dorset X Suffolk and Dorset X Columbia ewes, were well above average for lifetime net revenue on irrigated pastures as well. Suffolk crossbreds consistently performed better on irrigated than on hill pastures. While most ewes with Columbia-type inheritance were more efficient on hill than on irrigated pastures, this result was not always consistent.

Even more than most disciplines in the Animal Sciences, quantitative genetics is dependent upon models. Models, by definition, are abstractions of reality. Invariably they require simplifying assumptions, which should be but sometimes are not clearly specified. One thesis of this article, illustrated by examples, is that many of the assumptions upon which animal breeding theory and practice are based are not valid. Some proportion of research resources should be devoted to challenging or verifying those assumptions and following up those areas of enquiry suggested by the outcome of such research. A further thesis is that the selection of topics and priorities for animal breeding research should be a matter of choice by individual scientists and should not be determined by steering committees or directed by administrative fiat. Hopefully, the resultant mutation, cross-fertilization, assortment, recombination and selection of ideas that would result would bestow upon our discipline higher fitness from multiple-peak epistasis, and minimal danger of extinction (or petrification) from over-specialization. A final thesis is that true creativity by research scientists should be nurtured and rewarded and that work in traditional areas of breeding and quantitative genetics should be continued-but done better.

Within 32 crossbred group-management system-birth year subgroups, "selection in retrospect" was practiced based upon several ewe lamb traits, singly or in combination, to assess what the effect of such selection would have been on ewe lifetime production efficiency. Ewes were from two birth years, eight crossbred groups and two management systems. Ewe's type of birth, date of birth, actual and adjusted weaning weight (WWt and AWWt), postweaning weight (PWWt) and first yr gross income (FGROS) were the ewe lamb traits involved in the single trait paper selection schemes. Only the ewe lamb weights (WWt, AWWt and PWWt) caused a significant increase in the production efficiency of selected populations over those of the corresponding unselected populations. When postweaning weight was used jointly with the ewe's type of birth in an independent culling level selection scheme, both the group composed of heavier multiple-born ewes and the group composed primarily of single-born ewes were more productive than the group composed of lighter weight multiple-born ewes. Backward selection of the elite ewes having the best production efficiency also showed that the heavier the ewe lamb, the more efficient she was expected to be. Examination of ewes surviving the entire duration of the experiment failed to identify any early life trait that predicted longevity. Furthermore, surviving ewes were equally variable in their early life traits to the populations at large. Longevity, however, was positively related to lifetime efficiency.

Three-hundred mature Panama-type range ewes were mated to Clun Forest, Dorset, Border Leicester, Polypay and Suffolk rams during the 1979 and 1980 breeding seasons. Sire breed and ram within breed effects on lamb growth, ewe reproduction, spermatozoan midpiece length (MPL) and midpiece length coefficient of variation (MPLCV) were examined. Associations among MPL and MPLCV and economically important traits also were assessed. Suffolk-sired lambs weighted .18, 2.0 and 1.5 kg more, at birth, weaning and post-weaning, respectively, than the average of all groups. Dorset-sired lambs had the lightest postweaning weight. Variation was greatest among Suffolk rams for average weaning and postweaning weights of their progeny. The Border Leicester breed had the least among ram variation for progeny weaning weight; while variation among Dorset rams was least for progeny postweaning weight. Fertility (ewes lambing/ewe exposed) and prolificacy (lambs born/ewe lambing) of the rams' mates were not influenced significantly by sire breed. Lamb mortality also was not influenced by breed of sire nor by rams within a breed. For variation in MPL, 26.4% was due to the breed effect (P less than or equal to .01) and 21.6% was attributable to ram variation within a breed (P less than or equal to .01). Clun Forest rams had the longest average MPL and greatest MPLCV, while Dorsets had the shortest MPL and smallest MPLCV. There were no important associations between either MPL or MPLCV and any of the economic traits.

From 1979 through 1987, British breed and crossbred cows were mated to Simmental, Pinzgauer or Tarentaise bulls or to Hereford-Angus crossbred bulls. Beginning in 1982, continental European crossbred females also entered the herd, to be mated for first calving to Hereford-Angus or Angus bulls and as cows to continental European or Hereford-Angus bulls. In progeny of British breed and crossbred cows, dam breed effects on birth and weaning weight were not important, but continental European crossbred calves were heavier than British crossbred contemporaries at birth and weaning. Pinzgauer- and Simmental-sired calves were heavier at birth than Tarentaise crosses, but calves sired by each of the continental breeds had similar weaning weights. Maternal heterosis was greater than direct heterosis effects on weaning weight (8% vs 5%), but only direct heterosis (13%) influenced birth weight. Within progeny of continental European crossbred cows, calves with a Tarentaise maternal grandsire were lighter at birth, with no significant difference among other maternal grandsire breeds. Maternal breed effects on weaning weight were not significant. Nevertheless, in contemporary years, continental European crossbred cows reared calves that were 10% heavier than calves reared by British crossbred cows. Pacific Northwestern cattle producers could achieve substantial increases in weaning weight from introducing inheritance from continental European dual-purpose breeds into cow herds and calf crops of British ancestry.