Effect of different levels of rumen undegradable protein and conjugated linoleic acid on performance of growing goat kids

Conjugated linoleic acids contain a mixture of linoleic acid isomers. Dietary conjugated linoleic acid supplementation to ruminant diet affect their metabolism. Conjugated linoleic acid have many beneficial biological properties including the reduction in fat deposition and increasing lean tissue and feed efficiency in various animals. On the other hand, fast growing ruminants require sufficient amounts of essential amino acid in the small intestine. There is no information regarding response of growing ruminant to the interaction of rumen undegradable protein and rumen protected conjugated linoleic acid, hence this experiment was aimed to study the interaction of rumen undegradable protein and rumen protected conjugated linoleic acid on performance, protozoa population and in vitro gas production in growing goat kids.

Thirty-two Kurdish male and female kids (average body weight 13.06 ± 1.08 kg; 4 months age) were used in a randomized block design with a 2 × 2 factorial arrangement. The fattening period lasted for 100 days including a 20-d of adaptation. Animals were fed total mixed rations three times a day. All experimental diets contain 15% crude protein and 2.4 Mcal ME/kg DM. Rumen undegradable protein of feeds was measured by in situ method using two rumen fistulated rams. Experimental diets contain 25 and 35 percent of rumen undegradable protein without or with 1.5 percent of rumen protected conjugated linoleic acid. Dry matter intake, average daily gain, feed efficiency, protozoa population and in vitro gas production parameters were measured. For total protozoa populations counting and genera differentiation, samples of rumen liquor were collected three hours after morning meal by stomach tube on day 70 of experiment. Rumen liquor samples were taken from two rumen fistulated rams which were fed on maintenance level. These rumen samples were collected before morning meal.

The results showed that kids fed diet containing 35 percent rumen undegradable protein supplemented with rumen protected conjugated linoleic acid had the greatest average daily gain (112.72 g/day), feed efficiency (0.21) and the lowest dry matter intake (564.72 g/day). Ruminal fluid total protozoa population did not affected by dietary treatments. Diet containing 25 percent rumen undegradable protein without conjugated linoleic acid supplementation had the highest potential gas production (497.76 ml/g OM) and maximum gas production (11.80 ml/g OM) per hour. Diet containing 35 percent rumen undegradable protein with conjugated linoleic acid supplementation had the greatest gas production half life (35.69 h) and the lowest time to reach maximum gas ptoduction (5.27 h).

Overally, diet containing 35 percent rumen undegradable protein and 1.5 percent rumen protected conjugated linoleic acid supplementation improved growing goat kids performance.