Cassava foliage as a protein source for cattle in Vietnam

The aim of the thesis was to evaluate biomass yield and chemical composition of cassava foliage as influenced by harvesting height and cutting interval (Paper I), the effect of different supplemental levels of dried, ensiled or fresh cassava foliage on rumen fluid parameters, thyroid gland hormones and liver enzymes of cattle fed urea treated fresh rice straw (Paper II to IV), and to determine the changes in live weight gain, thyroid hormones and liver enzymes of heifers supplemented by different levels of dried, ensiled or fresh cassava foliage (Paper V). The experiments were carried out at the experimental farm of Nong Lam University, Ho Chi Minh City, Vietnam, on fistulated cattle of local yellow breed (Paper II to IV), growing heifers of Sindhi breed (Paper V), and at the field crop station (Paper I). In Paper I, harvesting height and cutting interval influenced the yield of cassava foliage and root tubers and to a lesser extent the nutritional quality of foliage. The highest dry matter foliage yield was 8 times higher at a harvesting height of 30 cm above the ground and 45 day cutting intervals, as compared to only one cut of the green foliage tops at the end of the season. The reverse was seen for tuber production on the same treatments, with only 28% of tuber yield at the highest foliage production. In Paper II to IV, almost all of the cassava foliage was consumed. Mean values of ruminal pH ranged from 6.14 to 7.03. Average NH3-N concentration ranged from 10.41 to 16.25 mg 100 g-1 of ruminal fluid, volatile fatty acids concentration ranged from 80.9 to 93.4 mmol L-1 of ruminal fluid, and both increased with higher amounts of cassava foliage in the rations. Serum triiodothyronine, thyroxin, free thyroxin, thyrotropin-stimulating hormone, alanine aminotransferase and aspartate aminotransferase concentrations were not significantly affected by ensiled cassava foliage and dried cassava foliage. When feeding fresh cassava foliage the triiodothyronine and thyroxin concentrations were lower, and alanine aminotransferase, aspartate aminotransferase and thyrotropin stimulating hormone concentrations were higher. Significant effects of fresh cassava foliage levels were found on triiodothyronine and thyroxin. In Paper V, increasing supplemental levels of ensiled cassava foliage and pelleted cassava foliage increased live weight gain, while the gain was not significant for fresh cassava foliage. Ensiled cassava foliage and pelleted cassava foliage supplements increased the daily weight gain by approximately 50% at the lowest supplementary level of 50 g CP 100 kg-1 LWt day-1 and by 100% at the highest supplementary level of 100 g CP 100 kg-1 LWt day-1. Thyroid hormones and liver enzymes did not differ among treatments with ensiled cassava foliage and pelleted cassava foliage. A significant effect of fresh cassava foliage levels was only found for triiodothyronine, while the levels of thyroxin, free thyroxin, thyrotropin-stimulating hormone, alanine aminotransferase, and aspartate aminotransferase were not significantly affected by fresh cassava foliage level. Results indicated that pelleted cassava foliage and ensiled cassava foliage could be safe protein supplemental sources for growing heifers without adverse effects on their performance.