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1501
Diet starch content and fermentability affects feed intake and milk yield of cows in the postpartum period
The objective of this study was to evaluate the effects of diet starch content and fermentability fed during the postpartum (PP) period on DMI, yields of milk (MY) and milk components, and body reserves. Fifty-two multiparous Holstein cows were used in a randomized block design with a 2 X 2 factorial arrangement of treatments. Diets were formulated to 22% (LS) or 28% (HS) starch with dry ground corn (DGC) or high moisture corn (HMC) as the primary starch source. Treatments were fed from 1 to 23 d PP and then switched to a common diet until 72 d PP to measure carry-over (CO) effects. Treatment period (TP) diets were formulated for 22% forage NDF and 17% CP, and starch concentration was adjusted by substitution of corn grain for soyhulls. The diet for the CO period was formulated to 20% forage NDF, 17% CP and 30% starch. Throughout the experiment both DMI and MY were measured daily, and milk components, BCS and back fat thickness (BFT) were measured weekly. During TP, DGC increased DMI by 2.2 kg/d compared with HMC (P<0.01) but tended to increase DMI more with HS (3.4 kg/d) than LS (1 kg/d, interaction P=0.12). Treatments also interacted over time; DGC increased DMI throughout the TP for HS but only after the first week for LS compared with the HMC treatments (P<0.01). There was no main effect of starch content on DMI. The effect of corn source diminished over time during the CO period (p=0.03) with no main effects of treatment on DMI. DGC increased yields of milk by 2.6 kg/d (P=0.12), 3.5% fat-corrected milk (FCM) by 4.3 kg/d (P=0.02), fat by 165 g/d (P=0.03), and protein by 165 g/d (P=0.01) compared with HMC with no effect of starch content throughout the TP. Starch source and content interacted (P< 0.05) to affect yields of fat and FCM during the CO period which were greater for DGC-HS and HMC-LS (1.78 and 52.1 kg/d, respectively) than for DGC-LS and HMC-HS (1.62 and 48.6 kg/d, respectively). DGC tended to decrease BCS loss until the third week of TP (P<0.15) compared with HMC but had no effect overall. No effects of treatment were detected for BFT during TP but HMC increased BFT 0.1 mm (P=0.04) during the CO period. Ruminal fermentability of starch is an important consideration for diets of cows in the PP period.
Keywords: high moisture corn, dry corn, fresh cows