The objective of this study was to analyze the genetic evolution of milk production, udder morphology, and animal behavior of Gir dairy cattle. Data were obtained on the predicted breeding values for milk yield of 60,226 cows born from 1968 to 2015 and standardized predicted breeding values for udder conformation and milking behavior of 7,635 cows born from 1987 to 2015. The influence of tested bulls on genetic trends was discussed, with special focus on the period after 1993, the year when the predicted breeding values of the first group of tested bulls were released. The traits of interest were 305-d milk yield, fore udder attachment, rear udder height, rear udder width, teat length, teat thickness, ease of milking, and reactivity. Significant genetic evolution was observed for 305-d milk yield, with increasing annual growth observed from 1993, as the number of cows sired by the best proven bulls increased. Before 1993, no genetic evolution was observed for any of the studied traits. From 1993 onward, all traits showed genetic gains, except fore udder attachment. The use of geneticallytested bulls since 1993 has led to important genetic gains in the Brazilian Dairy Gir population. Before the identification of genetically superior bulls began, many traits showed no improvement. Selection for milk yield has modified the conformation traits of the Gir mammary system. The longevity of the mammary glands of high-yield cows may be impaired due to poor fore udder attachment. Regarding behavioral traits, this population has evolved to less-reactive animals that are easier to milk.
ContextThe body condition score (BCS) is an easily measured, fast, inexpensive, and non-invasive tool to estimate the amount of body fat and to evaluate the nutritional status of dairy cows.AimsThe aim of this study was to validate BCS in primiparous Gyr cows by using ultrasound measurements of subcutaneous fat (FT).MethodsBody weight, BCS (score of 1–9) and FT measured at five body sites (FT1–FT5) were recorded during the prepartum and postpartum periods. Linear regression of FT on BCS and Pearson’s correlations were used.Key resultsThe correlations between body weight and FT measures ranged from 0.49 to 0.63 and from 0.51 to 0.64 during the pre- and postpartum periods respectively, while the correlations between BCS and FT ranged from 0.69 to 0.82 and from 0.67 to 0.78 in the two periods. The BCS better reflected the variation in FT before and after calving than did body weight. Linear regression models were used to explore the relationship between BCS and FT measurements considering the former as the predictor variable. The coefficients of determination (R2) obtained for the prepartum variables ranged from 0.48 to 0.67. The highest R2 was obtained for the model that included FT measured in the lumbar region midway between the last rib and tuber coxae (hook; FT4) as the response variable. The R2 of the models whose response variables were obtained during the postpartum period ranged from 0.45 to 0.60. The highest R2 was observed when the pelvic region midway between the tuber coxae (hook) and tuber ischii (pin; FT2) was used as a response variable.ConclusionsThe correlations between BCS and FT validate the use of BCS obtained by visual assessment as a tool for evaluating fat reserves in Gyr dams before calving and during first lactation. Among the FT measurements, FT2 and FT4 are interesting because both are easy to measure and showed higher correlations and coefficients of determination with BCS before calving and lactation.ImplicationsThe BCS is an accessible tool for producers that requires only training of the evaluator and that is economically viable since no special equipment is needed.
All content in this magazine is licensed under a Creative Commons Attribution License. Attribution-Non-Commercial-Non-Derivatives 4.0 International (CC BY-NC-ND 4.0). CORRELATION BETWEEN TESTICULAR MORPHOMETRIC MEASURES, SEMINAL QUALITY, LIBIDO, MORPHOLOGICAL CHARACTERISTICS AND TEMPERAMENT OF BREED BULLS ''GIR LEITEIRO''
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