JWSS - Journal of Water and Soil Science

Feed shortage is one of the most important characteristics of Iranian livestock industry. Therefore, the utilization of agricultural by-products in animal nutrition, especially for fattening animals, is of great importance. In order to study the effect of the four rations containing various levels of tallow (0, 2.5, 5, and 7.5%), on the performance of male Holstein calves (MHC), responding to the above treatments 1, 2, 3 and 4, twenty four MHC (191±32.1 kg) at age 6-7 months-old in a completely randomized design were used. The calves were fed individually for 195 days ad libitum.

Average daily gains (ADG) of the MHC fed diets 1, 2, 3 and 4 were 1.56, 1.61, 1.69 and 1.75 kg (P<0.05), respectively. Feed conversions (as DM) were 4.63, 4.31, 41.2 and 3.98 (P<0.05), respectively. Added tallow to the ration did not affect carcass, empty body weight (EBW), but increased warm carcass weight (P<0.05). The dietary treatments did not increase digestibility (D) of dry matter organic matter, crude protein and gross energy either, but decreased D of neutral detergent fiber and increased apparent crude fat (P<0.05).

Effects of the β-adrenergic agonist metaproterenol were studied daily gain, carcass composition and feed consumption of Varamini female lambs were studied. Thirty lambs were randomly assigned to a randomized complete block design with three groups (treatments) and two blocks (live weight). The ration was similar for all groups (ME: 2.6 MCal/kg, CP: 14.9%) and lambs were fed ad libitum. Metaproterenol was injected subcutaneously at 0 (control), 7 (low dose) and 14 (high dose) µg kg^-1 w⁷⁵. Lambs were weighed at 20-day intervals.

Mean daily weight gain and feed conversion ratio improved significantly by metaproterenol (P<0.05), but feed intake was not affected. Hot carcass weight, carcass weight minus fat-tail, dressing percentage and longissimus muscle characteristics were different among the three groups (P<0.01). Physically separated fat from several depots and fat-tail weight significantly reduced in the metaproterenol groups. Carcass fat content decreased but carcass protein content increased in metaproterenol treated lambs.