title: Corn silage hybrid type and quality of alfalfa hay affect dietary nitrogen utilization by early lactating dairy cows.
abstract: This experiment was conducted to determine the effects of corn silage (CS) hybrids and quality of alfalfa hay (AH) in high-forage dairy diets on N utilization, ruminal fermentation, and lactational performance by early-lactating dairy cows. Eight multiparous Holstein cows were used in a duplicated 4 × 4 Latin square experiment with a 2 × 2 factorial arrangement of dietary treatments. The 8 cows (average days in milk = 23 ± 11.2) were surgically fitted with ruminal cannula, and the 2 squares were conducted simultaneously. Within square, cows were randomly assigned to a sequence of 4 diets: conventional CS (CCS) or brown midrib CS (BMR) was combined with fair-quality AH [FAH: 46.7% neutral detergent fiber (NDF) and 18.4% crude protein (CP)] or high-quality AH (HAH: 39.2% NDF and 20.7% CP) to form 4 treatments: CCS with FAH, CCS with HAH, BMR with FAH, and BMR with HAH. Diets were isonitrogenous across treatments, averaging 15.9% CP. Each period lasted a total of 21 d, with 14 d for treatment adaptation and 7d for data collection and sampling. Intake of DM and milk yield did not differ in response to CS hybrids or AH quality. Although feeding BMR-based diets decreased urinary N output by 24%, it did not affect fecal N output. Feeding HAH decreased urinary N output by 15% but increased fecal N output by 20%. Nitrogen efficiency [milk N (g/d)/intake N (g/d)] tended to increase for BMR treatments. Ruminal ammonia-N concentration was lower for cows fed BMR-based diets than for those fed CCS-based diets but was not affected by quality of AH. Feeding BMR-based diets or HAH decreased milk urea N concentration by 23 or 15%, respectively, compared with CCS-based diets or FAH. Total volatile fatty acid concentration increased with HAH but was not influenced by CS hybrids. Feeding BMR-based diets decreased urinary N-to-fecal N ratio (UN:FN), and it was further reduced by feeding HAH. Although cows fed the BMR-based diets tended to increase milk N-to-manure N ratio, the quality of AH did not affect the ratio. The lower ratio of UN:FN with a higher ratio of milk N-to-manure N ratio for the BMR-based diets indicates that feeding BMR may reduce manure ammonia-N by reducing excretion of urinary N and increasing secretion of milk N per unit of manure N excreted.
authors: Department of Animal, Dairy, and Veterinary Sciences, Utah State University, Logan 84322.
authors: M S
authors: MS
authors: Holt
authors: K
authors: K
authors: Neal
authors: J-S
authors: JS
authors: Eun
authors: A J
authors: AJ
authors: Young
authors: J O
authors: JO
authors: Hall
authors: K E
authors: KE
authors: Nestor
mesh_terms: D000818:Animals; D002417:Cattle; D004032:Diet / Q000662:veterinary*; D004043:Dietary Fiber / Q000378:metabolism; D005232:Fatty Acids, Volatile / Q000378:metabolism; D005243:Feces / Q000737:chemistry; D005260:Female; D005285:Fermentation; D007774:Lactation; D008372:Manure; D000455:Medicago sativa; D008892:Milk / Q000737:chemistry; D009584:Nitrogen / Q000378:metabolism*; D012417:Rumen / Q000378:metabolism; D012820:Silage; D003313:Zea mays
chemical_list: D004043:Dietary Fiber; D005232:Fatty Acids, Volatile; D008372:Manure; D009584:Nitrogen
keywords: alfalfa hay; brown midrib corn silage; dairy cow; nitrogen excretion