Two hundred eight-eight weanling pigs (initially 12.31bs and 18 d of age) were used in a 27-d growth assay to determine the interactive effects of Zn source and feed grade medication on growth performance. Experimental treatments were arranged in a 2 x 3 factorial with main effects of medication (none or 50 g/ton of carbadox) and Zn source (none, 250 ppm of Zn from a Zn amino acid complex, or 3,000 ppm of Zn from ZnO). The results suggest that dietary Zn improved growth performance primarily from d °to 14 and feed grade medication improved growth performance from d 14 to 27. Pigs fed diets containing ZnO had better growth performance than pigs fed diets containing no additional Zn, and pigs fed diets containing ZnAA had intermediate responses.
The relationships between body condition score (BCS) observed during late first lactation and the first 45 days of second lactation and two measures of feed efficiency, residual feed intake (RFI) and gross efficiency (GE) defined as milk energy / DMI, measured during mid first lactation were assessed in 173 Holstein cows. Body condition score was compared between the 18 most and least feed efficient cows. When measured as RFI, feed efficient cows carried significantly more condition at dry off and tended to carry more condition at the start of second parity and at 45 days in milk (DIM), but there was no difference in change in BCS between feed efficient and inefficient cows. When measured as GE, efficient cows tended to carry less condition 30 days prior to dry off and lose more condition throughout the first 45 DIM. These findings suggest that selection based on RFI should not impact BCS change during late first lactation or early second lactation but selection based on feed efficiency measured as GE may result in greater BCS loss in early second lactation.
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