Predicting the effect of proteolysis on ruminal crude protein degradation of legume and grass silages using near-infrared reflectance spectroscopy.

Two studies were conducted to assess whether routine applications of near infrared reflectance spectroscopy could predict the effects of silage proteolysis on ruminal crude protein (CP) degradation of legume and grass silages. A preliminary study was conducted to assess the effect of laboratory drying method on ruminal CP degradation of silages. Thirty legume and grass silages were freeze-, oven-, or microwave-dried and incubated in situ in the ventral rumen of three ruminally cannulated cows for 24 h. Freeze-drying was considered least likely to alter ruminal CP degradation of the silages; therefore, oven- and microwave-drying were compared using first-order regression with freeze-drying. Oven-drying for 48 h at 55 degrees C compared favorably (R2 = 0.84) with freeze-drying. Microwave-drying resulted in a large bias (2.84 g/10(-1) kg of CP) and was poorly related (R2 = 0.48) to freeze-drying. In a second study, alfalfa and timothy were cut at three maturities and allowed to wilt for 0, 10, 24, 32, 48, and 54 h. Forages were ensiled in triplicate cylindrical mini silos and allowed to ferment for 120 d. After fermentation, silages were oven-dried, ground, and scanned on a near-infrared reflectance spectrophotometer. Duplicate, dried, 2-mm ground silage samples were incubated in the ventral rumen of three ruminally cannulated cows for 24 h. Forage species, maturity, and wilting time significantly affected 24-h ruminal CP degradation of the silages. Near-infrared reflectance spectroscopy accurately predicted (R2 = 0.91) 24-h ruminal CP degradation of silages. Data suggest near-infrared reflectance spectroscopy can accurately assess the effects of forage species, maturity, and wilting time (proteolysis) on 24-h ruminal CP degradation of legume and grass silages.

Prediction of laboratory and in situ protein fractions in legume and grass silages using near-infrared reflectance spectroscopy.

Legume and grass silage samples (n = 121) were collected from commercial forage testing laboratories (trial 1). Samples were dried at 55 degrees C for 48 h, ground, scanned on a near-infrared reflectance spectrophotometer, and analyzed for crude protein (CP), soluble CP, acid detergent fiber (ADF) CP, and neutral detergent fiber (NDF) CP by wet chemistry methods. Sixty samples were selected for calibration development, and the remaining samples were used for equation validation. Near-infrared reflectance spectroscopy accurately predicted the CP content of the silages (R2 = 0.96), but prediction of soluble CP, ADF CP, and NDF CP was markedly less accurate. The coefficients of determination and standard errors of calibration for CP, ADF CP, NDF CP (percentage of DM), and soluble CP (percentage of CP) were as follows (0.96 and 0.80, 0.77 and 0.24, 0.72 and 0.71, and 0.82 and 4.40). In a second study, legume and grass silage samples (n = 32) were dried at 55 degrees C and ground (2 mm). Duplicate dacron bags containing 5 g of silage were incubated in the ventral rumen of three ruminally cannulated cows for 0, 3, 6, 12, 24, 48, and 72 h. In situ protein fractions, including rapidly degraded protein, slowly degraded protein, undegradable protein, degradation rate, and rumen-undegradable protein, were determined. Original samples were reground (1 mm) and scanned. Previously defined near-infrared spectroscopy calibration procedures were conducted. Coefficients of determination for in situ CP fractions were R2 > 0.92 with the exception of degradation rate (R2 = 0.87). Data suggest that in situ protein fractions are better predicted by near-infrared reflectance spectroscopy than by laboratory protein fractions.

Development of a novel system to estimate protein degradability in legume and grass silages.

Five trials were conducted to develop a system to estimate rumen-undegradable protein (RUP) of legume and grass silages using near infrared reflectance spectroscopy. In situ procedures were the reference method used to determine silage RUP content. Trials 1, 2, and 3 were devoted to improving in situ procedures. In trial 1, alfalfa silage with and without heat treatment was incubated ruminally in 30 cows. The standard deviation of in situ RUP attributable to cow and diet was 0.82 and 3.80 g/10(-1) kg of crude protein (CP) for the unheated and heated alfalfa, respectively. Based on trial 1, it was determined that 8 cows would be required to establish RUP standards. In trial 2, low (13.3 g/10(-1) kg of CP) and high (44.5 g/10(-1) kg of CP) RUP standards were developed using eight ruminally cannulated cows. In trial 3, 11 new RUP standards were developed by mixing trial 2 RUP standards together. The RUP standards were used to employ a calibration curve technique in ruminally cannulated cows. The technique was employed in four ruminally cannulated cows to estimate RUP contents of 121 silages, and RUP values were used for near-infrared reflectance spectroscopic analysis in trial 4. Trial 4 procedures yielded a calibration for RUP content of silages with an R2 of 0.84 and a standard error of calibration of 1.55 g/10(-1) kg of CP. In trial 5, the equation was tested on 300 silage samples. The mean predicted RUP content was 21.8 g/10(-1) kg of CP. Data suggest near-infrared reflectance spectroscopy can predict RUP content of silages.

Performance of lactating dairy cows fed red clover or alfalfa silage.

The objective of this study was to compare utilization of red clover (Trifolium pratense L.) and alfalfa (Medicago sativa L.) by lactating dairy cows. Red clover and alfalfa were harvested and conserved as silage at two maturities in 2 consecutive yr. Each year, diets containing experimental forages and supplemental grain were fed to 16 multiparous Holstein cows in early lactation in a replicated 4 x 4 Latin square lactation trial. Lactation performance and nutrient intake responses caused by forage type (red clover vs. alfalfa), maturity (early vs. late), and equivalent acid detergent fiber (ADF) content (yr 1, late alfalfa vs. late red clover; yr 2, early alfalfa vs. late red clover) were compared. Milk yield was not different between cows fed red clover or alfalfa in yr 1, but milk yield was higher for cows fed red clover in yr 2. When cows were fed alfalfa and red clover with similar ADF content, the milk yield of cows fed red clover was lower than that of cows fed alfalfa in yr 1, and milk yields were similar between cows fed alfalfa and red clover in yr 2. Milk protein yield and percentage were lower for cows fed red clover in yr 1 and 2, respectively. Intake of ADF and neutral detergent fiber was lower for cows fed red clover in both years. When red clover contained the same ADF content as did alfalfa, cows fed red clover ate less ADF, neutral detergent fiber, and dry matter, resulting in lower milk yield potential.

Effect of accelerated postpubertal growth and early calving on lactation performance of primiparous Holstein heifers.

Seventy postpubertal Holstein replacement heifers were assigned to one of four treatments to assess effects of accelerated postpubertal growth on performance during first lactation. Heifers were fed control or accelerated diets from 10 mo of age until parturition, and breeding was initiated at 14 or 10 mo of age, respectively. Heifers were also subdivided into two breeding groups (target or delayed) based on normal AI breeding efficiencies. Heifers fed accelerated diets had a higher average daily gain (933 vs. 778 g/d) and calved earlier (21.7 vs. 24.6 mo) than did heifers fed control diets. Heifers fed accelerated diets had similar prepartum (10 d) BW, but lower wither height and postpartum BW, than heifers fed the control. For heifers fed accelerated diets, milk fat and milk protein yields were lower, and milk fat percentage was higher, at mo 1 and 2; milk fat percentage was lower at mo 3 to 7 of lactation. Delayed bred heifers calved later (approximately 2 mo), had higher prepartum and postpartum BW, and were taller at the withers than target bred heifers. Delayed breeding resulted in higher body condition scores at calving and a greater incidence of dystocia, but lactation performance was not affected. Accelerated postpubertal growth resulted in earlier calving at similar prepartum BW, but data for wither height, pelvic area, and postpartum BW suggested that heifers fed accelerated diets were smaller. Accelerated postpubertal growth and early calving reduced performance during first lactation, but the exact mechanisms could not be determined.