Characterisation of the lactation curve of Gyr and Sardo Negro cattle

Abstract

The objectives were to characterize the lactation curves (LC) of tropical Gyr and Sardo Negro (SN) cattle from Mexico for the design of breeding and management programs for these breeds. A total of 3561 records of 504 lactations and 3927 records of 449 lactations were used for Gyr and SN, respectively. Three lactation lengths (LL) were evaluated, namely 240 (240d), 270 (270d), and 300 (300d) days, with five non-linear models (NLM): Wood, Wiltmink, Cobby, Brody, and Sikka. Milk production was obtained at the beginning (PI; kg), daily average (PMD; kg), maximum at peak (PMX; kg), days to reach maximum production (DP), and accumulated total (PT; kg). The selection of models was made based in the Akaike and Bayesian information criteria. The NLM explained at least 88% of the variability in the data. Brody model provided the best fit for 240d and 270d, and Sikka for 300d in SN; for Gyr, Wood model showed the best fit for 240d and 270d, while Wiltmink had the best fit for 300d. The means for PMD were 5.3 kg in SN and 10.2 kg in Gyr; for PMX the averages were 6.9 kg and 12.7 kg, respectively. The average of PT, within LL (240d, 270d, and 300d), was 1297 kg, 1418 kg, and 1552 kg for SN, and 2653 kg, 2930 kg, and 3202 kg for Gyr, respectively. The first third of the LC presented the highest contribution (%), with average values of 37.4 in Gyr and 39.5 in SN; the second and third periods, contributed (%) 33.5 and 29.1 in Gyr, and 33.0 and 27.5 in SN, respectively. The 240d LL, are the proposals for the design of management, feeding, and genetic improvement programs, they presented the best statistical adjustment in both breeds.