
TY  - JOUR
A1  - Graham, NM 
A1  - Searle, TW 
T1  - Energy and nitrogen utilization for body growth in young sheep from two breeds with differing capacities for wool growth
JF  - Australian Journal of Agricultural Research
JO  - Aust. J.  Agric. Res.
Y1  - 1982
VL  - 33
IS  - 3
SP  - 607
EP  - 615
KW  - 
UR  - https://doi.org/10.1071/AR9820607 
N2  - Utilization of energy and nitrogen was assessed by serial slaughter and intake/loss balances, and wool growth was measured, as young sheep grew from c. 25 to 30 kg on either 700 or 1000 g/day of a high-protein diet. Comparisons were made between animals with low (Dorset Horn) and high (Corriedale) propensities to produce wool. Depending on feed intake, fleece-free liveweight gain was 102-215 g/day in the Dorsets and 88-172 g/day in the Corriedales; corresponding growth rates of clean dry wool were c. 5 and 10 g/day, there being little effect of feed intake. Digestibilities of protein and energy were 84 and 74% respectively in both breeds at the lower level of feeding; at the higher level the values were 80 and 71 % in the Dorsets and significantly lower, 77 and 69 %, in the Corriedales. Metabolizable energy was 83 ¦ 0.3 % of digestible energy at the low intake and 86 ¦ 0.5 % at the high intake in both breeds. It averaged 11.7 ¦. 0.07 MJ/kg feed dry matter, being 0.2 MJ/kg more at the low than at the high intake and, in the latter case only, 0.3 MJ/kg more in the Dorsets than in the Corriedales. At the low and high levels of feeding respectively, the fleece gained 0.18-0.16 MJ and 0.93-0.89 g nitrogen daily in the Dorsets compared with 0.31-0.34 MJ and 1.65-1.81 g nitrogen daily in the Corriedales. The corresponding average daily retentions in the body were 1.74-2.46 MJ and 1.80-3.49 g nitrogen in the Dorsets and 1.34-2.08 MJ and 1.25-3.07 g nitrogen in the Corriedales. Thus body growth accounted for 91-94% of the energy retention and 6640% of the nitrogen retention in the Dorsets, but only 81-86 % and 43-63 % respectively in the Corriedales. The composition of weight gain was the same in both breeds and 15-20% of the energy stored in the body was in protein. It is estimated that the marginal efficiency of use of metabolizable energy was 31-34% for body growth and 16-19% for wool growth. It is concluded that, given a high protein diet, animals with a strong propensity to grow wool diverted an appreciable amount of metabolizable energy from body growth to wool production, thereby restricting deposition of both fat and protein. 
ER  -

