Some Factors Affecting Weight Gains of Dairy Heifers Fed All-Roughage Rations

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Abstract
Factors affecting weight gains by dairy heifers were studied with 28 heifers on pasture and ten individually fed heifers on either an all hay or grass silage ration. The heifers averaged about 450 1b. in weight. The only factor significantly correlated with gains on pasture was forage dry matter digestibility (r=.797). On pasture, the multiple correlation between average daily gains and dry matter digestibility, dry matter intake, and body weight was .831. Over a 56-day feeding period, the correlations between dry matter intake and average daily gains were .711 for silage and .399 for hay. Correlations between body weight and dry matter intake were .932 for silage and .857 for hay. Multiple correlations between average daily gains, body weight, and dry matter intake were .858 for silage and .463 for hay. Respective average daily gains for pasture, silage and hay were 1.79, .92, and 1.34 lb. The error of estimate of weight gains in all groups prevents accurate estimate of response from factors measured and emphasizes the large number of animals required to show significant differences between rations. On an individually fed hay ration, 82, 14, and 4 animals per treatment were required to show significant differences in average daily gains of .10, .25, and .50 lb. between group means. On silage 174, 28 and 7 animals were required to show the above differences. When the effects of body weight and dry matter intake of silage were removed, the number of animals needed was reduced to 72, 12, and 3. The data would appear to indicate that intake was a major factor only on grass silage.