Variation in individual piglet birth weights in a Large White × Landrace sow herd

Within-litter birth weight variation in pigs is increasingly becoming important in influencing the profitability of pig enterprises. The objective of the study was to characterize within-litter birth weight variation in piglets from Large White × Landrace sows. The study was conducted using records from 1 768 litters collected between January 1998 and September 2010 from a pig herd in South Africa. The number of piglets born alive (NBA) ranged from three to 18. The mean within-litter birth weight coefficient of variation (CVBWT) was 17.6% and ranged from 0.47% to 50.7%. The distribution of CVBWT in the herd was positively skewed. CVBWT increased as NBA increased. Multiparous sows farrowed litters with higher CVBWT than gilts. To enhance profitability of pig enterprises, the selection for increased NBA should be followed by selection for decreased CVBWT.Keywords: Coefficient of variation, litter weight at birth, number of piglets born alive, parit

Random regression test-day model for the analysis of dairy cattle production data in South Africa: Creating the framework

Genetic evaluation of dairy cattle using test-day models is now common internationally. In South Africa a fixed regression test-day model is used to generate breeding values for dairy animals on a routine basis. The model is, however, often criticized for erroneously assuming a standard lactation curve for cows in similar contemporary groups and homogeneity of additive genetic variances across lactation and for its inability to account for persistency of lactation. The random regression test-day model has been suggested asa more appropriate method and is currently implemented by several Interbull member-countries. This review traces the development of random regression methods and their adoption in test-day models. Comparisons are drawn with the fixed regression test-day model. The paper discusses reasons for suggesting the adoption of the random regression approach for dairy cattle evaluation in South Africa and identifies the key areas where research efforts should focus