Genetic trends for 305-day milk yield (P305) in Brazilian Guzerat herds under selection were compared. Data from 4898 lactations of 3179 purebred and crossbred cows from various regions of Brazil were used. Milk yield was adjusted for mature age and the contemporary groups were defined as herd and calving year. Genetic parameters were estimated using the MTDFREML program. The model included the...

some factors affecting crude protein balance (cpb), as a measure of efficiency, were studied using 2824 records of 501 lactating holstein cows. the cpb (kg d-1) was calculated as crude protein (cp) intake (kg) minus cp yield (kg). two different statistical methods including principal components (pcs) and general linear model analyses were used to study the effects of different factors. crude pr...

Twelve spring-calving and twelve winter-calving cows were managed for extended lactation cycles of 18-months duration, with the former group then completing a second extended lactation. Half of the cows were fed according to standard management practice for the herd; the other half received supplementary concentrate from week 9 of lactation onwards. Commencing at the same time, half of the udde...

Decisive heifer management for improved lactation and reduced dystocia requires a systematic analysis of age, body weight (BW), and average daily gain (ADG) using an adequately large sample size. The objective of this study was to determine effects of BW and age at first breeding and ADG until pregnancy on yields of milk, milk fat, and milk protein in the first lactation and the occurrence of d...

Emphasis on milk yield (MY) as well as milk yield persistency (MYP) and calving interval (CI) is necessary to achieve more sustainable productionin dairy cattle. Therefore the main objective of this study was to find an optimum regression model to estimate economic values for MY, MYP and CI.Using a deterministic bio-economic model, seventyfiveproduction states differing mainly in MY, MYPand CIw...

in order to evaluation of genotype by environment interactions in holstein cows, iran was divided into cold, middle cold, temperate and hot climate regions. for this purpose used from 39570, 35813 and 18955 records for milk, fat and protein yields, respectively, to progeny test for 35 sires that have 50 daughters in each climate. the data were collected by the centre of breeding and improvement...

the objective of this study was to investigate the effect of principal components (pc) of the regression coefficients (co)variance matrix on the lactation curve, and on the formation of selection index to modify the curve, based on these pc’s, and as well to estimate additive genetic and phenotypic variances and heritability of the constructed selection index. lactation period of 301 d (5-305) ...

Dairy heifers had an estimated grazed pasture intake of either 11.8 (H) or 6.0 (L) kg DM/heifer/day for four weeks in early lactation and a common pasture allowance thereafter. Group L produced less milk (2202 vs. 2433 R) and milk protein (75.0 vs. 81.6 kg) than Group H in 31 weeks but milk fat yield (104.9 vs. 109.8 kg) and milk composition were not significantly affected. All heifers lost bod...