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Zebu breeds play an important role in cattle production systems in Brazil. To assess the genetic variability from animals in the Herd Books of Nelore, Gir and Guzerat breeds, generation intervals, inbreeding, effective population size and parameters of gene origin (effective number of founders, ancestors and founder genomes) were calculated using pedigree records from 1938 to 1998. Breed subdivision was quantified by Wright’s F-statistics. Calculations were separately carried out for consecutive 4-year intervals in the period 1979–98. Generation interval was around 8 years for the three breeds. Total inbreeding increased in all the breeds reaching values of 2.13%, 2.28% and 1.75%. Effective population size decreased from 85 to 68 in Nelore, from 70 to 45 in Gir and remained nearly constant around 104 in Guzerat. The quantities assessing the number of contributing ancestors decreased with time in all the breeds, and in the last analysed period the most important ancestor accounted for 14%, 3.1% and 4.1% in Nelore, Gir and Guzerat, respectively. Results indicate that the studied breeds are suffering from a loss of genetic variability which can result in negative effects on breeding and conservation purposes. [ABSTRACT FROM AUTHOR]

The main stream dairy breeds suffer a continuous process of fertility and health decay, due to genetic antagonism with the high milk yield attained through the very successful selection for this trait, as food intake did not sufficiently increase to meet initial lactation requirements inducing negative energy balance. Selection for angularity (dairy form) aggravated the problem, because it resulted in lower body condition cows and inbreeding depression also concurs to the negative outcome. In addition, a negative genetic correlation between milk yield and heat tolerance has been shown in Holsteins. Correcting course seems sensible. However, given the present commercial structure, it seems unlikely that this may be effectively done by selection. Shifting to new breeds, such as the New Zealand Friesian and Jersey and the Norwegian and Swedish Red, might be preferable, particularly in the Latin-America context, where high yield systems are not prevalent and crossbreeding has proved profitable. [ABSTRACT FROM AUTHOR]

Lifetime dairy production, reproduction and growth traits of 75 females sired by Holstein, Jersey or Brown Swiss bulls and Holstein-Friesian x Gir dams of 1/2 to 3/4 Holstein-Friesian fractions were compared. The animals were in a single herd under the same management. Milk, fat and protein yields, concentrates fed, reproduction, and weights were recorded throughout the lifetime of the cows. The data were analyzed by least squares techniques under models including the fixed effects of breed of sire, Bos taurus fraction and year of birth. Herd lifes for Holstein, Jersey and Brown Swiss crosses were 6.006 +/- 0.812, 8.129 +/- 0.863 and 7.247 +/- 0.777 years. Milk yields per day of herd life were 7.150 +/- 0.266, 6.757 +/- 0.282 and 6.249 +/- 0.254 kg. Weights of cull cows sold were 458 +/- 15, 415 +/- 15 and 457 +/- 13 kg. Based on these and on previously reported results of the same experiment, intakes of roughage and pasture were estimated from energy requirements. Lifetime expenditures on concentrates, roughages, pastures, milking, reproduction, and heifer rearing were calculated based on mean performance of each breed of sire, as well as on receipts from animals and milk sold (the latter with four sets of prices of protein, fat and carrier). The conclusion was that in systems of artificial female calf rearing and male calf wastage, the Jersey crosses appear to offer important economic benefits to farmers, which would be even greater if payment on milk protein and fat becomes effective.

Serial data on live weights, height at withers and the weight/height ratio of 263 cows (3 to 9 years old) and 196 heifers (2 to 5 years old) were studied. The animals were of six red and white Holstein-Friesian (HF)/Guzera crosses (1/4, 1/2, 5/8, 3/4, 7/8 and > or = 31/32 HF-expected gene fraction). Separate analyses were performed for cows and heifers using the Proc Mixed of the SAS package. Models included the fixed effects of farm, season, reproductive and lactation status, two-factor interactions, quadratic regressions on age and age x crossbred group interaction, as continuous co-variables and regressions on the HF gene fraction and on breed heterozygosity, plus the animal random effect. Only heifer growth in height and weight/height was linear with age. In all three traits in both categories the individual additive-dominance model explained the variation between crossbred groups. The breed additive difference was not significant (P > 0.05) for cow and heifer live weight and for heifer weight/age ratio. Heterosis was significant for all traits except height of cows. Linear and quadratic regression coefficients for cows, were, respectively, for live weight, 35.20 +/- 5.23 kg/year and -1.54 +/- 0.43 kg/year2, for withers height, 2.49 +/- 0.29 cm/year and -0.15 +/- 0.02 cm/year2 and for weight/height, 0.22 +/- 0.04 kg/cm/year and -0.01 +/- 0.003 kg/cm/year2. Corresponding values for heifers were, for live weight, 153.46 +/- 37.06 kg/year and -15.69 +/- 4.91 kg/year2, while only linear coefficients applied to withers height (1.63 +/- 0.43 cm/year) and weight/height (0.16 +/- 0.03 kg/cm/year).

The liveweights of 100 females sired by Holstein (H), Jersey (J) or Brown Swiss (BS) bulls out of Holstein-Friesian x Gir dams of 1/2 to 3/4 Holstein-Friesian fraction were compared. The animals were kept in a single herd under the same management. The data were analyzed separately for four age categories by least squares techniques. The models for cows and heifers older than 18 months included the fixed effects of breed of sire, Bos taurus fraction, season of weighing, days in milk class (for cows only), pregnancy status class, year and the random effect of animal nested within breed of sire x B. taurus fraction subclasses. The models for younger heifers included the same effects except for lactation and pregnancy status. Based on 2937 observations, the mean weights for 0- to 6-month-old calves for the groups with H, J or BS sires were 88 +/- 1, 77 +/- 1 and 75 +/- 1 kg, respectively, the mean weights for 1-year-old heifers were 168 +/- 2, 159 +/- 2 and 155 +/- 1 kg, for 2-year-old heifers, 327 +/- 4, 303 +/- 4 and 319 +/- 4 kg, for 3-year-old heifers, 380 +/- 5, 369 +/- 8 and 390 +/- 4 kg and for cows, 464 +/- 3, 413 +/- 2 and 478 +/- 2 kg. Cubic growth curves, which were different in the three sire breed groups, satisfactorily explained the cow weight changes with age (R(2)>or=0.98). Maximum weight was attained at 7.8, 9.5 and 9.2 years in cows with H, J or BS sires. Although breed of sire effects were not significant in heifers (P>0.05), those with H sires were the heaviest up to two years of age. The females with BS or J sires had similar weights up to one year of age, but thereafter the former reached similar weights as the females with H sires and declined less after attaining the maximum weight. The cows with J sires were the lightest at all ages. Since previous results showed similar protein and fat yields per day of calving interval in the three breed of sire groups, it is suggested that the lighter J crosses may be more economic than the other groups on account of their likely lower feed maintenance costs.