Abstract
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 day in milk [DIM]), were studied 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). Crude protein digestibility of the 10.5% CP diet was lower (p<0.05) than that in diets with higher levels of CP, while there were no significant differences among the other three levels of CP (12.5, 13.7 and 14.4%). Daily milk yield tended to increase with increased CP from 10.5 to 14.4%. Income over feed in terms of USS/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 (NH 3 -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 as indicators 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.
Highlights
Feeding of dairy cattle in the tropics is often difficult because of deficiencies in feed supply, in both quality and quantity (Wanapat and Devendra, 1992)
Experimental design and treatments Thirty two, multiparous Holstein Fresian crossbred dairy cows, ranging from 100-150 days in milk (DIM) and yielding between 10-15 kg/day were used in a Randomized complete block design (RCBD) to determine the effect of four levels of crude protein (CP) by varying the levels of cottonseed meal
Nutrient and dry matter intake (DMI) There were no significant differences among treatments, these results being similar to a report of Christensen et al (1993, 1994) who showed that intakes of DM were not altered by level (14.2 to 19.6%) of dietary CP
Summary
Feeding of dairy cattle in the tropics is often difficult because of deficiencies in feed supply, in both quality and quantity (Wanapat and Devendra, 1992). The use of rice straw as a feed in the dry season, in spite of its low nutritive value, has been a common feeding system, generally practiced by dairy farmers in the tropics when green forages are often scarce (Leng and Preston 1983; Wanapat, 1994). Cottonseed meal (CSM) is a by-product from oil extraction and is a source of rumen by-pass protein supplement in dairy cattle feeding (Grings et al, 1991; Wanapat et al, 1996). Cottonseed meal has been used at 8.6% of a total mixed ration in dairy cattle diets, and could increase feed
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