Brokken (1971a,b), McDonough (1971 and Scott and Broadbent (1972) using linear programming (LP). Optimal weights for buying and selling feedlot cattle have been considered in addition to optimal feeding programs by Meyer and Newett (1970) and Kennedy (1972)

SUMMARYData for 432 litters of pigs were collected from 1965 to 1975 inclusive, at the Fasola Stock Farm, near Oyo in the Western State of Nigeria. The breeds represented were Large White, Duroc and Hampshire, and their crosses. The main objective was to investigate the effects of certain identifiable environmental sources of variation on litter performance characteristics such as litter size, mortality and weight at birth, 3 weeks and 8 weeks of age. Breed and year effects were significant for the litter size traits, but parity of dam, season and breed × season effects were significant only for litter size at birth which increased up to the fifth parity and then declined steadily in subsequent parities. Postnatal pig mortality was affected significantly by breed, litter size at birth and breed × season interaction. It was found that the larger the size of litter at birth the higher the postnatal mortality. Average pig weight at birth was reduced by approximately 0·01 kg for each additional pig in the litter.

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Gestation periods taken from 432 records on purebred Large White, Duroc, Hampshire and their crossbred sows at Fashola Stock Farm in the Oyo State of Nigeria were analysed to determine the effects of some factors on the trait. For Large White, Duroc, Hampshire and the crossbred sows the mean gestation periods were 113.2, 115.1, 114.5 and 112.8 days respectively. Overall least squares mean was 11.2 days with a standard deviation of 9.06 days. Litter size at birth, year of birth and breed x season interaction had very highly significant effects of length of pregnancy. Breed differences were significant (P less than 0.05) whereas parity and season per se did not seem to influence this trait. Effects of boars accounted for some 11.8% of the trait was estimated as 0.47 r - 0.20 while the repeatability coefficient was 0.13. The data indicated a slight negative association between gestation period and litter size at birth.