Relação entre características morfológicas e produção de leite em vacas da raça Gir

Abstract

Resumo -O objetivo deste trabalho foi determinar parâmetros genéticos relacionados a características morfológicas e suas correlações genéticas com a produção de leite, em vacas da raça Gir. Utilizaram-se 3.805 registros provenientes de 2.142 vacas. O modelo utilizado na análise de características morfológicas continha os efeitos fixos de rebanho, ano e estação de classificação, estádio da lactação e idade da vaca à classificação, além da identificação do classificador. Quanto à produção de leite, foram incluídos no modelo os efeitos fixos de rebanho, ano e estação de parição e idade da vaca ao parto. Os parâmetros genéticos foram obtidos por meio do aplicativo REMLF90. As estimativas de herdabilidade variaram de 0,09 a 0,54. A variabilidade genética aditiva da maioria das características é suficiente para que ganhos genéticos anuais significativos possam ser alcançados com o processo de seleção. As correlações genéticas entre as características morfológicas variaram de baixas a altas e, entre elas e a produção de leite, de baixas a moderadas. Altas correlações genéticas entre algumas características morfológicas implicam a possibilidade de exclusão de algumas delas do programa de melhoramento genético da raça Gir, no Brasil. As correlações genéticas entre produção de leite e algumas características morfológicas indicam que estas podem ser utilizadas na formação de índices de seleção.Termos para indexação: características de conformação, correlação genética, Gir leiteiro, índices de seleção, parâmetros genéticos. Relationship between morphological traits and milk yield in Gir breed cowsAbstract -The objective of this work was to determine genetic parameters related to morphological traits and their genetic correlation with milk yield of Gir breed cows. A total of 3,805 records from 2,142 cows was used. For morphological trait analysis, the used model included the herd fixed effects, classification year and season, lactation phase and animal age at evaluation, besides the classifier identification. For milk yield, the fixed herd effects, year and season of calving and cow age at calving were included in the model. The genetic parameters were estimated using the REMLF90 software. The heritability estimates varied from 0.09 to 0.54. The additive genetic variability of the majority of traits is sufficient to achieve significative annual genetic gain by selection practices. The genetic correlations among morphological traits varied from low to high and, between them and milk yield, from low to moderate. High genetic correlations among some morphological traits implies on the possibility of exclusion of some of them from the breeding program, for Gir breed in Brazil. The genetic correlations between milk yield and some morphological traits indicate that they may be used in the formation of selection indexes.

Genetic Association Between Herd Survival and Linear Type Traits in Holstein Cows Under Tropical Conditions

“…The posterior mean of heritability for linear type traits obtained in conjunction with each measure of longevity (Long1_60, Long1_72, Long2_48 and Long2_54) showed low variation, which for the most part were 0.01 and 0.02 points, except for stature (0.04) and body depth, rump angle, foot angle and udder cleft that showed variation of 0.03 (Table 4). Low heritabilities for hoof angle (0.10) and udder texture (0.11) were also observed by Campos et al (2012) in Holstein cows, as well as by Němcová et al (2011) and Lagrotta et al (2010) in Holstein and Gir cattle, respectively, for hoof angle (0.09 and 0.12). The posterior residual correlations were low, ranging from -0.05 to 0.09 (Table 5).…”

“…Thus, allowing the permanence of highly productive cows for a longer period in the herd, as well as reduced replacement of these animals, may result in an increased selection intensity with animals of higher genetic values (Silva et al, 2003;Lagrotta et al, 2010).…”

“…Among the type traits, those related to the mammary system may be considered as the most important due to the genetic association with milk production (Rennó et al, 2003;Lagrotta et al, 2010) and longevity (Zavadilová et al, 2009). The low posterior genetic correlations between final score and survival measures indicate that genetic gains for longevity will be insignificant if selection is based exclusively on the final score, although this trait is used as selection criteria by Brazilian farmers (McManus and Saueressig, 1998).…”

“…Cows that have a long herd life result in increased opportunities for voluntary disposal based on production and the reduction of involuntary culling due to reproductive problems, health or locomotion (Berry et al, 2005), thus creating higher selection intensity (Lagrotta et al, 2010). Stability or survival in the herd was defined by Hudson and Van Vleck (1981) as the probability of cows remaining in the herd until a certain age.…”

Genetic parameters for longevity measures in Brazilian Holstein cattle using linear and threshold models

“…Longevity is important in the dairy industry as herds with longerlived cows, show greater opportunity to return revenue (Queiroz et al 2007), but also show a lower number of replacements, and consequent decrease in involuntary culling, increasing culling related to milk production which results in herds with higher genetic merit for milk production (Lagrotta et al 2010). The average observed for Long2 (2.7), Long4 (60.08 months) and Long5 (33.45 months) were similar to those reported for Holstein cows in other countries.…”