Search

Three trials were conducted using ewe lambs to determine the effects of accelerated growth during rearing on reproduction and lactation. Data were obtained on 113 ewes. Early weaned ewe lambs were randomly assigned to the following prebreeding treatments: (1) thin (T, moderate gain) and (2) fat (F, accelerated gain). They were bred to lamb at 13 to 15 months of age. After breeding, one half of the ewes on the T and F treatments were switched to the other treatment so that postbreeding treatments were TT, TF, FF and FT. Prebreeding treatment did not affect conception rate (T, 95%; F, 96%), but lambing rates were 43, 28 and 27% higher (P0.05) for F than T ewes in trials 1, 2 and 3, respectively. Daily milk production was higher in T ewes than F ewes for each trial, but the differences were significant only in trial 3. Estimated daily milk yields over the 60-day period were: T ewes, 1482, 1571, 1614 g; F ewes, 1183, 1373, 1321 g for trials 1, 2 and 3, respectively. Number of alveoli also favored T ewes. Switching ewes to the alternate treatment after breeding did not affect reproduction or milk production. Correlations between weight to height ratio and milk yield were negative in trials 1 and 3 but were positive in trial 2. There was no indication that serum T(4) levels affected milk production or reproduction. The results of this study show that accelerated growth during rearing increased lambing rate but may impair milk production. These effects appeared to be fixed by the time the ewes were bred.

An experiment was conducted to measure the milk production response to increased frequency of milking and to mammary gland stimulation per se. A total of 25 cows was employed in two trials. The treatments compared were twice-daily milking (2 ×), four-times-daily milking (4 ×), and either two-times-daily milking plus hand stimulation without milking (2×H) or two-times-daily milking plus oxytocin injection (2×I) midway between each milking interval. Treatments 2×H and 2×I compared to treatment 2×resulted in a 1.0 to 1.5% nonsignificant increase in production. Treatment 4×resulted in a milk production increase of 7.9% over treatment 2 ×. Further, this increase was attained by the second day on the increased milking frequency. The rapidity of the production response, plus the lack of response to additional stimulations per se, suggests that stimulation→oxytocin→prolactin→increased milk synthesis is not the explanation. Rather, that frequent milking→reduced intramammary pressure→increased secretion is probably the explanation.

Twenty-four primiparous mice were divided into four equal groups. The four groups were randomly assigned to injections of .5, .25, and .125 IU of synthetic oxytocin or oxytocin solvent. Average daily body weights of mothers and pups were compared over 15 days postpartum. Mammary glands were removed and processed for histological examination. Average body weight gains of mothers were not significantly different among treatment groups. In general, there was no difference in average body weight gain of pups among treatment groups except that in the group nursing mothers injected with .5 IU oxytocin, average weights decreased slowly until by 12 days of age their weight gain adjusted for 4-day weights was less than the .25 and .125 oxytocin groups (P Milk production response to exogenous oxytocin injection is dependent both on amount of oxytocin administered and on duration and intensity of the suckling stimulus applied.

Summary Forty-eight animals from a Streptococcus agalactiae -free herd, after a 4-week standardizing period immediately after calving, were assigned to be milked from the fifth to the 44th week of lactation at either 10, 13.5, or 17 in. of vacuum and for a "normal" or "twice normal" duration. Of these animals, 24 were Guernseys and 24 Holsteins. Within each breed group, 12 were first-calf heifers and 12 had one or more previous lactations. Within each breed-lactation group of 12, six were selected for being "clean" of mastitis and six for being "infected." The following results were obtained: 1.No appreciable differences in milk yield and FCM were observed between vacuum levels. Milking time and time to reach peak rate of flow decreased in a linear manner and rate of milk flow increased. The least amount of time spent in stripping was at the 13.5 in. vacuum level, and the least amount of strippings, expressed as a percentage of the total yield, was at the 10-in. level. 2.Leaving the milking machine on the udder for an extended duration (twice normal) resulted in slightly greater yields of FCM (1.01b. per cow per day) and decreased stripping time. 3.In this experiment, mastitis infected animals gave greater milk yields and had slower rates of milk flow than did the mastitis clean animals. 4.The differences between first-calf heifers and animals with one or more lactations and between Guernseys and Holsteins agreed in general with previously published studies.

Eighteen primiparous mice in their 6th to 9th day of lactation were randomly divided into groups of six. Each group was assigned to one of the three milking intervals, .25, 4, and 12h. Blood flow was measured simultaneously in right and left abdominal mammary glands by Sapirstein's indicator fractionation technique with sodium 24 chloride as the indicator. Lactose was extracted from the same tissue and quantified by gas chromatography. Up to 4h, mammary blood flow was inversely related to the amount of milk accumulated in mammary gland. Around 4h blood flow started to level off and somewhere between 4 and 12h reached a maintenance rate. Rate of lactose synthesis was markedly reduced in this period. The relationship between mammary blood flow (Y) and lactose content (X) in the tissue was curvilinear, Y=4.43 − .83X + .06X 2 (correlation – .83).

The effects of rapid weight gain to puberty on reproduction, mammary development and milk production in ewes lambing at 13 mo of age were investigated on three trials. A total of 64 Dorset and 93 Suffolk ewe lambs were weaned at 42 d of age and their mean weight was 16 kg. These ewes were assigned, within breed groups, to either a finishing diet or a growing diet. Onset of puberty was determined by daily checks for estrus and ewes were bred beginning at 7 mo of age. In Trial 2, mammary gland development was determined in eight Suffolk ewes from each diet. Ewes on the finishing diet were younger at puberty than those on the growing diet (199 vs 206 d, P

The primary purpose of the present trial was an attempt to produce antibodies to autologous and homologous milk whey proteins in three ruminant species; moreover, to use rabbits as a source of heterologous antibody and to show that the preparation used for immunization was antigenic. The underlying thought was that since milk proteins are unique to the mammary gland, an auto-allergic condition to milk proteins may play a role in mastitis. Lactating females, virgin females, and males of the bovine, ovine, and caprine species were immunized with injections of a mixture of complete Freund's Adjuvant and whole milk. Eleven injections were given over a three-month period. The results showed the bovine did not produce antibodies to either homologous or autologous milk proteins. However, the ovine and caprine species produced both autologous and homologous antibodies of low concentration. Neither quarter milk production nor incidence of clinical mastitis was influenced by repeated injections of milk. It was concluded that the autologous and homologous antibodies produced against milk proteins were not important etiological agents in an auto-allergic condition of mastitis. It was postulated that the apparent unresponsiveness to injected milk proteins in the bovine may be due to intestinal absorption of large quantities of immunologically reactive milk proteins during the first few neonatal days. This, then, could cause an acceptance of milk proteins and failure to recognize these as being foreign in later life.

Estradiol-testosterone injection had similar lactation suppressing effects in sheep, goats and cattle. The depression in milk production was generally in proportion to the dose, although the extent and duration was influenced by individual animal characteristics. Cows and goats responded within three days, whereas, sheep required eight days for maximum depression. The net synthesis of fat, protein and solids-not-fat following injection was reduced. As expected, when milk production decreased, solids-not-fat and generally per cent protein increased, whereas, fat was somewhat more erratic and generally depressed. A stimulatory effect of the hormone on milk synthesis following the initial depression was evident. In subsequent lactations, there was no altered production. In addition, the milk was colostrum-like following smaller injections and was markedly altered (watery, clotted, etc.) following larger injections. The physical appearance was accompanied by relative increases in all whey proteins derived from blood (two times for albumin, and 20 times for immune and β 2 -globulins). Those synthesized in the mammary gland decreased to one-third for α -lactalbumin and to one-half for β -lactoglobulin. Possible effects of estrogen on suppressed lactation and altered composition during pregnancy were considered. Visible changes in the appearance of milk suggested that normal variations in endogenous hormone levels, especially during the estrous cycle, may influence milk leucocytes to a great extent.