Genetic parameters of a biological lactation model: early lactation and secretion rate traits of dairy heifers

Abstract

Early lactation parameters are difficult to estimate from commercial dairy records due to the small number of records available before the peak of production. A biological model of lactation was used with weekly milk records from a single Holstein herd to estimate these early lactation parameters and the secretion rate of milk from the average cell throughout lactation. A genetic analysis of the lactation curve parameters, calculated curve characteristics and secretion rate traits was undertaken. Early lactation traits were found to have little genetic variation and effectively zero heritability. Secretion rate traits for milk, protein, lactose and water were all moderately heritable and highly genetically correlated (.0.87) but fat secretion rate had lower genetic correlations with the other secretion rates. A similar pattern of correlations was seen between total lactation yield traits for fat, protein, lactose and water. The genetic correlations between the lactation curve traits and the secretion rate traits were calculated. Total milk yield, peak yield and maximum secretion potential were all highly correlated with milk, lactose and water secretion rates but less so with fat and protein secretion rates. In particular, fat secretion rate had a moderate to low genetic correlation with these lactation curve traits. Persistency of lactation was highly correlated with fat and protein secretion rates, more persistent lactations being associated with lower rates of secretion of these milk components. Similar levels of heritability were found, where trait genetic parameters were directly equivalent to those derived from the same dataset by random regression methods. However, by using a biological model of lactation to analyse lactation traits new insights into the biology of lactation are possible and ways to select cows on a range of lactation traits may be achieved.

The relationship between fertility and lactation characteristics in Holstein cows on United Kingdom commercial dairy farms

“…Day of peak yield is a trait usually reported with low heritability. The heritability estimate in this study was 0.03 and was lower than the 0.09, 0.09, 0.10, and 0.06 reported by Shanks et al (1981), Muir et al (2004), Farhangfar (2002), and Pollott (2009, respectively. Persistency was found to have a heritability of 0.10 and was low compared with other reports in the literature (Shanks et al, 1981;Batra et al, 1987;Jamrozik et al, 1998;Zwald et al, 2003;Muir et al, 2004;Pollott, 2009).…”

“…The trait with the highest heritability (0.36) was PY, which was higher than the 0.27 from a similar data set in Albarrán-Portillo and , and higher than the 0.30 estimated by Pollott (2009) because in the studies by both Albarrán-Portillo and and Pollott (2009), the heritability of MS was close to the heritability of PY (0.36). The heritability of PY was high compared with those reported by Farhangfar (2002) and Pollott (2009) and was within the range reported by Zwald et al (2003). The heritability of GM was 0.13.…”