Two experiments were carried out with the aim of defining relative value of different protein sources for milk production using tropical feed resources.
The first experiment was carried out on four fistulated multiparous Holstein Friesian crossbred (dry period ) dairy cows to evaluate nutritive value of local protein feed resources using the in sacco method and in vitro pepsin -pancreatin digestion. Measurements were made of ruminal degradability, intestinal digestibility of DM and crude protein, and effects of the rumen environment in cattle fed on untreated and urea-treated rice straw. Feeds used were cottonseed meal (CSM), soybean meal (SBM), dried brewer's grain (DBG), palm seed meal (PSM), cassava hay (CH) and leucaena leaf meal (LLM). Each feedstuff was weighed into duplicate nylon bags and incubated in each of the four rumen fistulated cows for 0, 2, 4, 8, 16, 24, and 48 h post feeding. Rumen feed residues from bags of 16 h of incubation time were used for estimation of lower gut digestibility by in vitro pepsin-pancreatin digestion.
Ruminal ammonia-nitrogen (NH3-N) concentrations were 4.5 and 12.4 mg% for untreated rice straw and urea-treated rice straw, respectively. Effective degradability of DM of CSM, SBM, DBG, PSM, CH, LLM in cows fed with untreated rice straw and urea-treated rice straw were 41.9,46.7; 56.1,63.3; 30.8,36.1; 47.0,48.3; 41.1,44.1 and 47.5,49.5 %, respectively. Effective degradability of the crude protein in cows fed with untreated rice straw and urea-treated rice straw were 49.6,54.6; 59.2,66.3; 40.9,48.8; 33.5,39.9; 47.3,54.6 and 65.0,70.6 % for the respective feeds. Both DM and crude protein in vitro pepsin-pancreatin digestibility of the same feed sources in cows fed with urea-treated rice straw were higher than in untreated rice straw . Results of crude protein in vitro pepsin-pancreatin digestibility, as ranked from the highest to the lowest, were SBM, CSM, LLM, CH, DBG and PSM for both environments.
It is concluded that the nutritive value of protein-rich supplements, in terms of rumen degradable, intestinal and total tract digestibility, was improved when urea-treated rice straw was offered as a roughage as compared with untreated rice straw; and that the lower ruminal ammonia concentration inhibited the degradation rate of the supplements when the cows were fed with low quality roughage (untreated rice straw). SBM and LLM were highly degraded in the rumen, while CH, CSM and DBG were less degraded and hence resulted in higher levels of rumen undegradable protein. These protein sources can be used to improve rumen ecology and rumen by-pass protein supply to ruminants.
The second experiment evaluated the effects of different levels of crude protein (CP) and cottonseed meal replacing for soybean meal in cassava chips and rice straw-based diets for mid-lactating cows (100 -150 d in milk [DIM], using 32 multiparous Holstein Fresian crossbred dairy cows. Diets containing 10.5, 12.5, 13.7, 14.4 % CP of the rations and 0 , 12.1, 14.9, 17.8 % cottonseed meal were fed to cows for 60 days. Thirty two cows were randomly divided into four dietary treatments using a Randomized complete block design. Four dietary treatments were offered in the form of total mixed ration (TMR) with concentrate to roughage (chopped rice straw ) at 60:40 and offered ad libitum.
Dry matter (DM) and neutral detergent fiber (NDF) intakes tended to linearly increase with increasing dietary CP levels. Intakes and digestibility of crude protein increased linearly with increasing dietary CP level (P<0.01) .CP digestibility of 10.5 %CP was lower (P<0.05) than that in higher level of CP,while there were no significant differences among the three levels of CP(12.5, 13.7 and 14.4 % CP). Daily milk yield tended to increase with increased CP from 10.5 to 14.4 %. Income over feed in terms of US$/kg of milk increased with increased CP from 10.5 to 13.7% and decreased when the CP level was higher than 13.7% (quadratic effect P < 0.09). Milk composition was not significantly affected by increasing level of CP, however there were relatively high contents of protein and fat among treatments.The proportion of milk-urea N (MUN), ammonia-N (NH3-N) and blood-urea N (BUN) were closely correlated and increased linearly with increasing CP levels (P<0.01). Balanced diet was found in diet containing 12.5 and 13.7 % CP of the rations when BUN and MUN were used asindicators of the protein to energy ratio in the diet.
Conclusions can be made that increasing dietary CP levels from 10.5 to 13.7 % using cottonseed meal as the main source to completely replace soybean meal was beneficial to cows consuming rice straw and cassava chips based-diets. Increasing the CP level above 13.7% of total ration did not additionally improve milk yield and composition or net income.