Effects of Kenaf (Hibiscus Cannabinus) as a Substitative Feed on Lactating Dairy Cattle

Improvement of ruminant feeding system by using locally grown fodder has received much attention in the tropics. Recently, kenaf has been shown to be a valuable fodder for beef cattle and small ruminants, but information on its use for dairy cow is scanty. Hence, the overall objective of the thesis was to examine the potential of using kenaf as a substitute for alfalfa hay (AH) and soybean meal (SBM) in dairy cow rations. Three experiments were carried out to achieve the above objective. Experiment 1 consisted of two studies. In the first, yield and chemical composition of kenaf at different harvesting ages were determined. Kenaf showed a favorable potential yield and chemical composition as fodder. Dry matter (DM), crude protein (CP) and amino acid (AA) degradability and digestibility of kenaf were measured and compared to AH and SBM in the second trial. Dry matter, CP and AA of kenaf were largely degraded in the rumen, resulting in low ruminal undegradable nutrient and absorbable AA. Nutrient degradability and digestibility of 6 weeks old kenaf were comparable to AH. Nutrient availability of kenaf was less than SBM. The optimum level of substituting AH and the CP from SBM with kenaf in diets and its effect on growth performance and nutrient utilization of growing dairy heifers were examined in Experiment 2 which also consisted of two studies. In the first, four crossbred dairy heifers were randomly fed four diets which AH were substituted with kenaf at 0, 33, 66 and 100% in a 4 x 4 Latin square design of 21d periods. Total substituting AH with kenaf had a significant negative impact (P<0.05) on feed intake, digestibilities of DM, organic matter (OM), fiber components and microbial protein synthesis (MPS). In the second trial, another group of four crossbred dairy heifers were used to determine effect of substitution of the CP from SBM with the CP of kenaf at 0, 33, 66 and 100% in a 4 x 4 Latin square design. The results showed that nutrient digestibility and MPS were markedly affected (P<0.05) when one to two-thirds of the CP from SBM was substituted with the CP of kenaf. Therefore, kenaf can substitute AH or the CP from SBM up to about 66% in dairy heifer diets. Experiment 3 involved substituting AH and/or the CP from SBM with kenaf in lactating dairy cow diets. Eight lactating crossbred Sahiwal-Friesians were used in a 4 x 3 incomplete Latin square design with 15d periods. The diets were T1=control, T2=AH was substituted with kenaf, T3=the CP from SBM was substituted with the CP of kenaf, and T4=AH and the CP from SBM were substituted with kenaf and the CP of kenaf respectively. Feed intake, nutrient digestibility, milk yield and milk composition were significantly affected (P<0.05), and AA availability to the mammary gland tended to decrease with substitution of kenaf. Lysine or methionine was the first or second limiting AA for milk protein synthesis. Leucine and phenylalanine ranked third and forth respectively with increasing levels of inclusion of kenaf in the diets of lactating dairy cow.

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