- Voluntary feed intake, growth and efficiency of Afrino x Merino and Dorper x Merino lambs
|Last update: March 27, 2012 11:45:43 AM|
Voluntary feed intake, growth and efficiency of Afrino x Merino and Dorper x Merino lambs
P G Marais
Animal Production Research
Grootfontein College of Agriculture
Private Bag X529
Middelburg C P
The effective use of crossbreeding in intensive farming enterprises requires knowledge of the growth patterns and feed efficiency of available breeds or crosses over a range of feeding levels and physiological stages.
The efficiency with which feed energy is utilized in growing sheep is a function of feed intake, body composition and energy requirements for maintenance. This interrelationship between feed efficiency and its causal components is influenced by both animal and nutritional factors. Differences between cattle breeds in the composition of growth can be explained largely by differences in frame size. These differences tend to decline as growth proceeds, which suggest that the differences in energy requirements for growth also decline towards maturity. Apart from frame size most of the genotype variation in composition of growth of sheep can also be ascribed to production traits (woolled vs non-woolled breeds), early and late maturing abilities and climatic extremes.
The object of this study was to quantify the voluntary feed intake, growth and efficiency of two Merino crosses at comparable stages.
MATERIALS AND METHODS
In an experiment conducted at the Grootfontein College of Agriculture two different types of Merino crossbred lambs were used as experimental material, viz. Afrino x Merino (A x M) and Dorper x Merino (D x M). Ten lambs, 5 rams and 5 ewes of each of these Merino crosses were used. The lambs were born and remained on karoo veld with the ewes until weaning at ± 120 days of age. The mean weaning masses recorded were 32,33 kg (rams) and 27,69 kg (ewes) for the A x M and 29,74 kg (rams) and 26,73 kg (ewes) for the D x M crosses. There were no significant differences between the weaning masses of the crosses or those of the sexes.
During the trial the lambs were individually fed a ration consisting of 59% maize meal, 40% lucerne hay milled through a 13 mm sieve and 1 % calcium carbonate (Ca C03), with a metabolizable energy content of 10,26 MJ/kg and a crude protein content of 11,13%.
RESULTS AND DISCUSSION
In this study a percentage of the exponent αw, called mature mass, was used as basis of comparison. The growth interval considered was between 20 and 40% of mature mass.
According to Table 1 it is clear that the A x M cross had the highest intake and that the intake of rams was superior to that of ewes. The growth rate of A x M was also higher than that of the D x M cross.
For further clarification it was necessary to evaluate the protein and fat deposition in the body of each cross at the same mature mass. It then became clear that the A x M cross rams gained protein at a faster rate than the D x M cross rams. The differences between ewes were very small. In respect of the gain in fat deposition the A x M cross showed the highest values. It was also clear that the rams from the A x M cross had the highest growth rate in lean, while the values of the D x M cross ewes were the highest.
Béranger (1976) concluded that statistical variation is reduced when comparisons between genotypes (crosses) at the same percentage of mature mass or metabolic age are made, but does not account for all the variation. He further stated that the remaining differences are in the composition of gain and that the energetic efficiency of protein deposition is lower than that of fat. Moreover, as protein in lean is associated with three times its mass in water, in terms of gain in body mass, efficiency should theoretically increase as protein content of gain increases. Therefore animals such as A x M cross rams, with a high growth rate in lean would appear to be more efficient than the D x M cross lambs. In fact this is not the case, however, because the efficiency (ME intake/energy retention) of the two different ram groups was exactly the same. A possible explanation for this must be sought in the higher fat gain of the A x M cross rams.
The results in Table 1 indicate small differences in energy loss between the two crosses in spite of vast differences in body composition. The differences in sex groups are very small. Part of this energy loss is what is conventionally known as maintenance expenditure.
According to the results elicited, it can be argued that, in terms of efficiency, as defined here, either of the two crosses can be used. If mass gain, especially lean meat (with the bonus of a better quality of wool), is desired, the Afrino seems to be a more suitable breed for the purpose of crossbreeding. However, since this research was conducted under intensive conditions with high quality feed, one can only speculate on the outcome of a similar experiment on veld conditions.
BéRANGER C, 1976. Feed efficiency and genotype-nutrition interaction in growing animals, particularly in cattle for beef production. Proc. C.E.A. Collegium, Theix, 27-28 Sept. p 382.
Karoo agric 3 (6), 18-19