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Dairy Science Department, Louisiana Agricultural Experiment Station, Baton Rouge
ABSTRACT
Three digestion trials were conducted during the summer months at three different periods of permanent pasture (oats, rye grass, clovers, and volunteer grasses) growth from May through August, 1959. A combination of internal (lignin) and external (Cr2O3) indicators was used to determine digestibility and intake of grazed herbage as the only source of forage in the total ration of milking cows. Forage samples were collected regularly throughout the experimental period. Milk weights, pasture scores (quantity and quality), and ambient temperatures were recorded daily.
Milk production adjusted for expected decline in lactation was significantly higher (P < .05) in Trial I than in Trials II and III. The average forage digestion coefficients of 68.27% for dry matter, 68.41% for crude protein, 63.31% for crude fiber, and 77.66% for NFE were significantly higher (P < .01) in Trial I than those of 51.59, 39.15, 55.04, and 62.01% in Trial III, and 41.22, 31.18, 49.06, and 51.13% in Trial II, respectively. The average forage digestion coefficients for dry matter and nitrogen-free extract in Trial III were significantly higher (P < .01) than those in Trial II. The average herbage dry matter intake adjusted for body weight of 27.62 lb in Trial I was significantly higher (P < .01) than the average intakes of 13.36 and 14.19 lb in Trials II and III, respectively. Cows in Trial I gained 25.5 lb per cow for the 14-day trial period, which was significantly different (P < .01) from the losses of 32.1 and 20.6 lb per cow in Trials II and III, respectively.
Regression analyses indicated that pasture quality score was the only significant variable in predicting milk production among the variables studied. Thus, a simple method of pasture evaluation appears to be of benefit in determining when to commence supplemental summer forage feeding to lactating cows grazing permanent pasture as the sole source of forage.
1 The data are from a thesis presented by the senior author to the graduate faculty of Louisiana State University in partial fulfillment of the requirements for the Ph.D. degree.
2 Present address: Animal Nutrition Department, Commercial Solvents Corporation, San Jose, California.
3 Dairy Science Department, Louisiana Agricultural Experiment Station, Baton Rouge, Louisiana.
4 Iberia Livestock Experiment Station, Jeanerette, Louisiana.
5 Louisiana Agricultural Experiment Station, Statistician, Baton Rouge, Louisiana.
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