| Summary: | 碩士 === 國立中興大學 === 畜產學系 === 88 === The purpose of this study was to investigate the effect on lactating performance, plasma measures and ruminal characteristics in dairy cows by incorporating prilled fat (PF) and/or Zinc chelated-amino acids (ZnAA) to the ration in cool season.
In the experiment 1, twenty lactating Holstein cows (eight primiparous and four multiparous) with 68 DIM and 32.36 kg/day milk yield in average were assigned into a 4×4 Latin square according to lactation, gestation number and milk yield. Diet treatments were divided into four groups: (1) control, (2) the control diet added with Zn Met 0.13% and Zn Lys 0.1% (DM basis), (3) the control diet added with 2.5% (DM basis) prilled fat, (4) the control diet added with 2.5% PF and both of AAs. All diets were formulated to meet the nutrient requirement of dairy cattle (NRC, 1989) and were treated as isoprotein but varying in energy content. Cows were fed these diets for four 3-week periods. Milk yield and orts were recorded during the last week at each period. Milk and blood samples were collected at the same time. In the experiment 2, the effect of the same four diets as in the experiment 1 on canulated cows were investigated. Four non-lacting Holstein cows with ruminal and duodenal canulate were assigned into four groups randomly. Ruminal and duodenal fluid were sampled during the last three days at each period to analyze pH, ammonia nitrogen (NH3-N) and volatile fatty acid (VFA).
The results in the experiment 1 indicated that the cows in the first, third and fourth periods might suffer mild heat stress, and cows in the second period may suffer medium heat stress. Cows fed PF demostrated the trend to decrease dry matter intake (P=0.1151), but showed no effect on body weight change. Milk fat percentage and milk fat mass were not affected significantly by the dietary treatment. Cows fed ZnAA appeared the trend to increase milk-protein percentage, and demostrated that the zinc chelated-amino acids might have the ability to protect amino acids. There was no interaction between PF and ZnAA in lactating performance. In blood performance, added ZnAA decreased the concentration of plasma urea nitrogen (PUN) significantly (P=0.0161), however, the group added PF increased plasma cholesterol very significantly (P=0.0054).
In the experiment 2, the concentration of NH3-N and pH value in ruminal fluid were not affected by treatments (according to the same postprandial time). Group added both PF and ZnAA (group D) showed significantly lower acetate/propionate ratio than other groups, whereas, the highest milk-fat percentage appeared in group D.
It was concluded that: (1)Feeding cows with ZnAA (Zn-Met 0.13% and Zn-Lys 0.1% (DM basis)) in cool season decreased PUN significantly and showed the trend to increase milk-protein percentage. (2)There was no interaction between group added PF and group added ZnAA in lactating performance. (3)Group added both PF and ZnAA showed significantly lower acetate/propionate ratio than other groups, but it did not influence milk-fat percentage.
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