Food intake growth and body composition in australian merino sheep selected for high and low weaning weight 1. food intake food efficiency and growth

Thompson, J.M.; Parks, J.R.; Perry, D.

Animal Production 40(1): 55-70

1985


ISSN/ISBN: 0003-3561
DOI: 10.1017/s0003356100031858
Accession: 005476316

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Abstract
Changes in the pattern of food intake, food conversion efficiency and growth from weaning to maturity, were examined in 35 rams and ewes from flocks of Merino sheep selected for high (weight-plus) and low (weight-minus) weaning wt and from a randomly bred control flock. The sheep were individually fed a pelleted ration ad libitum for at least 72 wk and up to 90 wk post weaning. Weekly food intake was described as an increasing exponential function of age with a linearly declining asymptote, about which a regular oscillation occurred, and weekly body-wt gain was described as an increasing exponential function of weekly food intake, about which a regular oscillation also occurred. The oscillations in weekly foood intake had a period of about 52 wk and appeared to be largely associated with seasonal variations in temperature, with an increased food intake during winter and a decreased food intake during summer. The oscillations in both the food intake and body weight functions were of similar phase and period and it was suggested that the body wt oscillations were due to variation in gut-fill, a result of the seasonal oscillations in food intake. Selection for weaning wt changed the shape and magnitude of the food intake curve, with the weight-plus having a greater rate of food intake (i.e. appetite) in the early stages of growth and a greater asympote than the weight-minus animals. Selection for high and low weaning wt also resulted in an increase and a decrease in mature wt. Both strains had a similar growth efficiency, although when calculated as gross food conversion efficiency the weight-plus were higher than the weight-minus animals at the same body wt; there was no difference between strains at the same age. The rams had both a higher asymptote and a slower rate of decline in food intake than the ewes. Rams had a higher mature wt than the ewes, although ewes had a slightly greater growth efficiency. When calculated as gross food conversion efficiency, ewes tended to be lower than rams, when compared either at the same age, or at the same body wt. When the food intake curves were standarized for differences in mature size, strain differences in the magnitude of the food intake curves were reduced, although differences in the shape were still apparent. Shape differences in the food intake curves were reflected in the shape of the standardized growth curves, with the weight-plus maturing at a faster rate than the weight-minus animals. There was little difference between the sexes in the initial shape of the food intake curve, although at later ages ewes had a lower food intake than rams. There was little difference between the sexes in the shape of the standarized growth curves.