Environmental and genetic effects on the lactation curves of four genetic groups of crossbred Holstein-Zebu cows

Abstract

-The objective of this study was to evaluate the effects of genetic group and environmental factors, including farm of origin, season of calving and lactation number, on the individual lactation curves of 1,010 Holstein-Gyr, GuzeratHolstein, Holstein-Nellore, and Holstein-Zebu F1 cows on the experimental farms of the Agricultural Research Company in Minas Gerais (Empresa de Pesquisa Agropecuária de Minas Gerais, EPAMIG). Least squares analysis and the incomplete gamma function were used to investigate differences in early milk yield, peak milk yield, time from onset to the lactation peak, persistency, total milk yield and lactation duration. The highest early yields were observed for Holstein-Gyr and Holstein-Zebu, and the lowest were observed for Holstein-Nellore cows. Early yield increased with lactation number, and the lactations that began in the late rainy and early dry seasons had the highest early yield. The time between lactation onset and the lactation peak was longer for primiparous Holstein-Gyr and Holstein-Guzerat cows. The lowest yields at the lactation peak were observed for the first lactation number. The highest values of persistency were observed for the first lactation number in Holstein-Guzerat cows. Total production from Holstein-Gyr and Holstein-Zebu cows were higher by approximately 14% and 29% compared with Holstein-Guzerat and Holstein-Nellore cows, respectively. The highest total yields were observed in lactations beginning in the dry season. Total yield increased with lactation number. The shortest lactation periods were observed in lactations beginning late in the rainy season. The incomplete gamma function was used to fit the individual curves from the genetic groups evaluated. The total yield differences were linked to early yields and yields at the peak of lactation.

Lactation Curve Pattern and Prediction of Milk Production Performance in Crossbred Cows

“…The lower initial yield, peak milk yield, and greater persistency in the first parity than the subsequent parity in KF cows as observed in this study corroborate earlier reports [ 6 , 26 – 31 ]. This is expected because lactation curves of the first parity are characterized by a less peak milk production and a greater persistency in ruminants [ 11 , 20 , 24 ]. The decline in persistency of lactation with increase in parity order is attributed to age factor as older animals start their lactation at a higher level and had a rapid rate of decline in milk production due to regression of alveolar cells with advancement in age.…”

“…Further, first-calving animals have less body weight and maturation of mammary tissue is still active, which counterbalances decline in milk production [ 32 ]. During the first lactation, animal encounters unfamiliar situations, including the atmosphere of the milking parlor, presence of dairy farmer, and the milking procedures [ 24 ]. Thus variation in the initial milk yield in different parities could be due to addition of more number of alveolar cells (secretory cells) at each successive pregnancy which reach their maximum numbers at about the 5th calving and diminish gradually thereafter [ 33 ].…”

“…Further moderate to high heritability estimates for different lactation curve shape parameters suggest that these traits can be included in selection schemes [ 43 ]. It has been reported that the milk secretory tissue requires more time for peak activity in primiparous cows than multiparous cows due to reduced udder size, less digestive capacity, and directs partitioning of nutrients [ 24 , 41 ]. The high persistency is associated with a slow rate of decline in milk yield after peak production, while low persistency is associated with a rapid rate of decline in milk yield due to less feed intake [ 44 ].…”

Influence of breeds genetic composition on the quality of milk from primiparous cows

“…Milk production values higher than those obtained in this study were reported by Silva et al (2011) evaluating the production of milk from multiparous Holstein cows of small, medium and large size, with values from 30.56 to 31.07 kg/milk/day and average of 23.27 kg. Glória et al (2006) evaluated the effects of breeds genetic composition and environmental factors on milk production of Holstein-Gyr crossbred cows and observed that the breeds genetic composition directly reflects the increase in total milk production with increased contribution from Holstein breed.…”

Heterosis in the components of lactation curves of Girolando cows

“…In linear models, the parameters are linear functions of days in milk or of their transformation, and can thus be estimated by linear regression (Torshizi et al 2011). Non-linear models are non-linear in the parameters and they are more statistically and computationally demanding, due to non-linearity than their linear equivalent models (Gl oria et al 2012). The advantage of such models is that the parameters represent the ascending or descending parts of lactation curve (Varanis et al 2016), which allow attributing a biological interpretation to each parameter (Gl oria et al 2012).…”