Lactation curve, milk composition and metabolic status of goats from different genetic groups under tropical conditions

The objectives of this study were 1) to compare models to describe the lactation curve of the Saanen, Moxotó, and Anglo-Nubian 2) to evaluate the effect of genetic groups on production and composition milk and efficiency of mobilization of body reserves during lactation. Twenty-three multiparous goats, newly calved, were divided into three treatments (genetic groups: 9 Saanen, 8 Moxotó, and 6 Anglo-Nubian). The goats were randomly distributed in collective pens, under the same feeding conditions. Five mathematical models were used to adjust the lactation curves: Wood (WD); Papajcsik and Bodero (PB); Adapted from Papajcsik and Bodero (APB); Nelder (ND) and Wilmink (WM). To indicate the best fit, the model evaluation system software was used, performing additional analyzes with the observed and predicted values ​​for each fitted equation. There were differences (P 0.05) in the parameters a, b and c between the genetic groups in each mathematical model. The APB model is recommended for use in all genetic groups to evaluate milk yield (Y), following the parameters: Y = 1.196+0.0545×t×e (-0.038×t) for Saanen, Y = 0.297+0.031×t×e(-0.0462×t) for Moxotó and Y = 0.757+0.0554×t×e(-0.0417×t) for Anglo-Nubian. The results for average milk production during 27 weeks of lactation were 1.37; 0.37 and 0.9 kg d-1 for Saanen, Moxotó and Anglo-Nubian, respectively. Except for lactose, there was a difference (P 0.05) between the genetic groups for milk composition and plasma beta-hydroxybutyrate (BHB) levels. Considering milk composition, the Saanen, Moxoto and Anglo Nubiana presented the averages (%) for fat of 3.66, 6.75, and 5.10, protein 3.32, 4.97, and 4.18 and lactose 4.28, 4.46, and 4.39%, respectively. There was no effect (P 0.05) on B-HBO in response to days of lactation, but Saanen and Anglo Nubian goats had higher plasma levels of this metabolite compared to Moxotó goats. Saanen had a greater weight loss of 12.83 kg, which was verified at 35 days of lactation. Saanen and Anglo-Nubian animals have a greater ability to mobilize body reserves compared to Moxotó. APB model is adequate to describe milk production of goats in tropical areas.