Modelling Lactation Curves for Dairy Sheep in a New Zealand Flock

Abstract

Lactation curves were modelled for dairy sheep in a New Zealand flock, providing information on the lactation yields of milk, fat, protein, and lactose, corrected for 130 days of milking. From 169 ewes, a total of 622 test-day records were obtained during the milk production season of 2021-2022 (from October to January). The flock produced an average of 86.1 kg of milk, 5.1 kg of fat, 4.5 kg of protein, and 4.1 kg of lactose, and moderate to large coefficients of variation were observed (27-31%) for these traits. The lactation persistency of milk, fat, protein, and lactose yields ranged from 52.3 to 72.7%. Analyses of variance for total yield and persistency were performed with an animal model that included the fixed effects of age (parity number), litter size, coat colour, and milking frequency (days in twice-a-day milking) and random residuals. Age and milking frequency were the only factors that significantly affected the yields of milk, fat, protein, and lactose. Age significantly affected the lactation persistency of milk and lactose yields, whereas litter size affected the persistency of protein, and milking frequency affected the persistency of fat. This study on this single flock provides valuable experience for a larger-scale animal breeding programme in New Zealand.

Keywords: animal model; dairy sheep; lactation curve; lactation persistency; milk production.

Figure 1

Lactation curves for daily yields of milk (A), fat (B), protein (C), and lactose (D) in lactations of Dairymeade ewes of one (blue), two (green), three (purple), and four years old or older (orange), modelled using orthogonal polynomials of order 4 for milk and lactose yields and of order 5 for fat and protein yields.