Estimativas de herdabilidade e correlações fenotípicas, genéticas e de ambiente entre algumas características reprodutivas e produção de leite na raça Gir

Abstract

Os objetivos deste estudo foram estimar herdabilidades e correlações fenotípica, genética e de ambiente entre produção de leite (PL), idade ao primeiro parto (IPP) e intervalo de partos (IDP) na raça Gir, com emprego de análises uni e bicarácteres sob o método da máxima verossimilhança restrita, por meio de algorítmo livre de derivadas (MTDFREML), ajustando modelos-animal. O modelo matemático para estudar a PL incluiu os efeitos fixos de rebanho-ano de parto e época de parto e idade ao parto como covariável (linear e quadrática) e, além do resíduo, os efeitos aleatórios de animal e ambiente permanente. Para a IPP o modelo incluiu os efeitos fixos rebanho-ano de nascimento e época de nascimento, e efeito animal como aleatório. O modelo adotado para estudar IDP contemplou os efeitos fixos rebanho-ano de parto e época de parto e idade da vaca ao parto como covariável, e mais os efeitos aleatórios de animal, ambiente permanente e resíduo. Por meio de análises bicarácteres, as estimativas de herdabilidade foram, respectivamente: PL1 e IPP = 0,25 e 0,18; PL1 e IDP1 = 0,27 e 0,07; PL2 e IDP2 = 0,20 e 0,05; PL3 e IDP3 = 0,17 e 0,05. As estimativas de correlações fenotípica, genética e de ambiente foram, respectivamente: PL1 e IPP = 0,02, -0,29 e 0,11; PL1 e IDP1= 0,23, 0,52 e 0,19; PL2 e IDP2 = 0,26, 0,54 e 0,23; PL3 e IDP3 = 0,25, 0,13 e 0,27.

Genetic parameters of milk production and reproduction traits of Girolando cattle in Brazil

“…The heritability for AFC that was obtained in this study ($0.20) was within the range from 0.17 to 0.22 that was reported for Gyr cattle (Balieiro et al 2003;Santana J unior et al 2010). Nevertheless, it was lower than the estimates of 0.33, 0.48 and 0.70 that were reported for Holstein  Gyr, Brazilian dairy crossbred females (Bos taurusÂBos indicus), and Holstein  Boran cows, respectively (Vercesi Filho et al 2007;Fac o et al 2008;Haile et al 2009) and the estimates of 0.23-0.35 that were reported for Holstein cows in Brazil (Val et al 2004;McManus et al 2008a).…”

“…Studies about heritability for CI involving three calvings in crossbred cattle in Brazil are scarce in the literature. The estimates that were obtained in this study were lower than those described by Balieiro et al (2003), except at the third calving (0.08 vs 0.05) for Gyr cattle, and the value of 0.12 that was obtained by Silva et al (1998) for the first CI using Holstein cattle in Brazil. However, our estimates are close to those obtained for Holstein cattle in other latitudes (Ojango & Pollot 2001;Montaldo et al 2010).…”

“…Therefore, the selection process to increase milk yield would result in a greater precocity of heifers. The genetic correlation between 305MY and AFC that was obtained in this study is greater than that of -0.29, which was described by Balieiro et al (2003) in studies using Gyr cows, and that of -0.20 reported by Val et al (2004) for Holstein cows. However, our estimate is lower than those of -0.65 and -0.63, which were mentioned by Silva et al (1998Silva et al ( , 2001 for Holstein and crossbred Mantiqueira cows, respectively.…”

“…However, several studies indicate that genetic selection to increase milk yield has a response that is correlated with a reduction in fertility due to antagonistic genetic correlations between production and reproduction traits (Ojango & Pollot 2001;Pryce et al 2002;Makgahlela et al 2007;Sewalem et al 2010). Studies in tropical and subtropical regions have revealed unfavourable genetic correlation between milk production and fertility in Holstein cattle and their crossbreeds (Silva et al 1998;Lôbo et al 2000;Wenceslau et al 2000;Balieiro et al 2003). For the Girolando breed, no studies were found in the literature regarding genetic correlations between production and reproduction traits.…”

Reproductive efficiency and milk yield in Sindhi breed cattle

“…Table 2 shows the averages for milk yield (MY), lactation period (LP) and total milk yield (TMY) according to age at first calving (AFC), calving age (CA) and calving order (CO) among classes. There was no difference (P≥0.05) for MY among different classes for ACF (AFC1 -AFC6), Balieiro et al (2003), in a study with primiparous cows from Gyr breed with age of 45.52 ± 0.09 months, observed 2653.58 ± 6.28 kg of average for MY, in 305 days of lactation, while Herrera et al (2008) evaluated the same breed and observed that AFC classes between 24 and 61months (class 1 -24 to 36 months; class 2 -36 to 48 months; class 3 -48 to 61 months) yield 2170.24 kg in 305 days of lactation, whereas it can be concluded that AFC can influence the MY. Thus, lower AFC resulted in lower MY.…”