Effects of Protected Fat When Fed to Dairy Cattle and the Interaction Between Supplemental Fat and Antibiotics in Mixed Cultures.

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Title: Effects of Protected Fat When Fed to Dairy Cattle and the Interaction Between Supplemental Fat and Antibiotics in Mixed Cultures.
Author: Daves, Meredith Gail
Advisors: Joe Cassady, Committee Member
Vivek Fellner, Committee Chair
Jerry Spears, Committee Member
Abstract: Fat is added to diets of lactating dairy cattle as an affordable method of increasing the amount of energy available to the animals. Unsaturated fatty acids are desirable end-products of milk production. However, their presence in the rumen can be toxic to ruminal bacteria, which will then decrease digestion. Unsaturated fatty acids are biohydrogenated into saturated fatty acids by specific bacteria in the rumen, which will decrease positive benefits associated with their consumption. Our first study evaluates the efficiency of calcium salts VALFEED 100M and VALFEED 200 in protecting unsaturated fatty acids from biohydrogenation in the rumen and also observes the effects of these 'protected fats' on lactation performance. Twenty-eight Holstein cows in early lactation were divided equally into four different treatment groups: 1) Control (with no supplemental fat); 2) Prilled fat; 3) Calcium salt of VALFEED 100M; 4) Calcium salt of VALFEED 200. Fat supplements were added to diets in place of corn in the concentrate mix at 3.2% of total dry matter intake. Cows were housed in free stalls equipped with Calan gates. The cows were fed twice daily, at 0800 and 1500 in amounts to allow ad libitum consumption. Weekly feed samples were taken and dried in order to calculate daily dry matter intake. Milk production was measured daily, and milk fat and protein content were analyzed at days 30 and 90. Body weights were taken at the beginning (day 0) and the end (day 90) of the trial. Prilled and VALFEED 100M fat supplements decreased (P <0.05) dry matter intake. Body weights were higher (P <0.05) in cows fed the control diet than those fed the prilled and VALFEED 100M diets. VALFEED 200-treated cows had similar (P >0.10) body weights when compared to all treatment groups. Milk yield was highest in cows fed VALFEED 200 (37.1 kg/d), and cows fed prilled and VALFEED 100M diets had lower (P <0.05) milk yields than those fed the control diet (32.0 kg/d, 32.8 kg/d, and 35.1 kg/d, respectively). Feeding VALFEED 100M significantly decreased (P <0.05) milk fat percentage when compared to the control and prilled diets. VALFEED 200 feeding did not significantly alter milk fat percentage when compared to prilled and control diets. Both VALFEED 100 and VALFEED 200 decreased (P <0.05) milk protein percentage. Feeding VALFEED 100M and VALFEED 200 resulted in an increase (P <0.05) in the cis- and trans- isomers of oleic acid (C 18:1) content of milk when compared to the control and prilled treatments. Both VALFEED 100M and VALFEED 200 also increased (P <0.05) linoleic acid (C 18:2) content in milk fat. The addition of VALFEED 100 to dietary rations depresses milk fat percentage (P <0.05) and increases (P <0.05) the percentage of trans-fatty acids in the milk when compared to the addition of VALFEED 200, suggesting that VALFEED 100 is less inert in the rumen than VALFEED 200. As previously mentioned, fat can be used as a feed additive to provide additional energy for the diet, but it also affects ruminal fermentation by decreasing waste loss and increasing feed efficiency. Ionophores, such as monensin, are drugs that alter ion transport and concentration gradients in specific ruminal bacteria. In doing so, they are capable of altering rumen fermentation and improving feed efficiency. Bacitracin is a non-ionophore antibiotic that affects similar bacteria as monensin but has a different mode of action. It also increases feed efficiency in ways similar to monensin. But, when ionophores are added to diets supplemented with fat, ionophore efficiency decreases. This interaction stimulated interest in conducting our second study. The inclusion of fat and ionophore-antibiotics to experimental diets and the sequence of their addition were investigated. Rumen fluid collected from a dry, fistulated cow was incubated in 8 fermentors for a total of eight days. The first two days of the trial represent a stabilization period. On day three, two fermentors received monensin (50 ppm), two received bacitracin (50 ppm), and the other four received fat (4.4% of DMI). On day 6, one of the fermentors receiving monensin and one receiving bacitracin got fat. The other two continued receiving either only monensin or only bacitracin. Of the remaining four fermentors that were receiving fat, one received monensin, one received bacitracin and the other two continued to only receive fat. Methane and pH were recorded several times daily. Culture samples were taken on days 2, 5, and 8 for analysis of SCFA, LCFA, NH3, and PCR. There were no statistical differences (P >0.10) in acetate and propionate production (mM) among treatments. However, the concentration of butyrate was higher (P <0.01) in cultures treated with monensin when compared with cultures treated with bacitracin. The proportion of C 18:2 in rumen bacteria increased (P <0.05) when monensin was added prior to fat in comparison to when fat was added prior to monensin. Preliminary results indicate that the sequence of fat and antibiotic addition effects the growth of Gram- and Gram+ bacteria. The results from this study show that the sequence in which fat and ionophore-antibiotics are added to mixed rumen cultures can alter the response of bacteria to the additives.
Date: 2003-09-22
Degree: MS
Discipline: Animal Science
URI: http://www.lib.ncsu.edu/resolver/1840.16/663

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