Recovering lactating dairy cows from diet-induced milk fat depression using corn with different starch degradabilities

Abstract Text: Milk fat depression (MFD) is a condition where milk fat synthesis is impeded by ruminal biohydrogenation intermediates and continues to be a problem in the dairy industry. The objective of this experiment was to determine the effects of feeding a high or low rumen degradable starch diet after diet-induced MFD. Six rumen cannulated Holstein cows (416.58 ± 25.23 kg BW^0.75;184.33 ± 29.6 DIM) were utilized in a crossover design consisting of covariate, induction, and recovery periods. All cows were fed a high fiber control diet for 10-d during the covariate, then switched to a high PUFA and low fiber diet for 10-d to induce MFD. After induction, cows were switched to one of two recovery diets with the incorporation of low or high degradable starch corn sources [LDS:35%; HDS:75% 7h starch degradability] for 18-d. Samples were collected every 3-d throughout the duration of the trial. All dependent variables were analyzed using the PROC MIXED procedure of SAS including the covariate period as a fixed effect and repeated measures. Starch level was similar (25%; P=0.76) in all treatments, however, crude fat level was greater for the induction diet as compared to HDS and LDS (9.89 vs. 4.47 HDS and 4.92 LDS). There was no treatment effect on DMI but the effect of day on DMI was significant across treatments (P<0.01). No treatment differences were detected for CP, crude fat, ADF, starch, sugar, and ash intakes but there was a significant increase of all nutrient intakes on days 16, 22, and 28 (P≤0.01). Milk yield, protein, lactose, and solids-not-fat were not affected by treatment, but were markedly decreased by day (P<0.01). Milk fat decreased during induction (P<0.01) and was significantly reduced by day 7 and 10 (P≤0.01). Total fatty acids less than C16:0 and cis-9, trans-11 CLA were not affected by treatment, but increased on days 4, 7, and 10 of induction (P≤0.01). Trans-10, cis-12 CLA was not different for HDS or LDS, yet there was a tendency of days to differ (P=0.09), with day 7 and 10 of induction having a greater concentration. Milk fatty acid profiles of the recovery diets were similar, milk yield was not affected, and DMI did not vary by treatment during this experiment. This suggests that utilizing corn sources with starch degradability of up to 75% may be incorporated into rations to recover milk fat to normal levels. 

Keywords: Milk Fat Depression, PUFA, Starch Degradability