Abstract #412

Section: Ruminant Nutrition (orals)
Session: Ruminant Nutrition 4: Production and Efficiency
Format: Oral
Day/Time: Tuesday 3:00 PM–3:15 PM
Location: Junior Ballroom A

# 412
Effects of supplemental concentrate type on dry matter intake and milk solids production of mid-lactation dairy cattle grazing perennial ryegrass-based pasture.
M. Dineen^*1,2, B. McCarthy², F. Coughlan², P. Dillon², M. E. Van Amburgh¹, ¹Department of Animal Science, Cornell University, Ithaca, NY, ²Teagasc, Animal and Grassland Research and Innovation Centre, Moorepark, Fermoy, Co. Cork, Ireland.

The objective of this study was to evaluate factors limiting DMI and milk solid production in dairy cattle grazing perennial ryegrass-based pasture. Eighty dairy cows averaging 98 ± 25 DIM and 518 ± 64 kg of BW were assigned to one of 4 treatments in a randomized block design. Dietary treatments were perennial ryegrass (PRG; DM = 20%, CP = 14%, aNDFom = 44%), PRG plus 4.8 kg DM of citrus pulp and 0.075 kg DM urea (Citrus; DM = 39%, CP = 13.5%, aNDFom = 38%); PRG plus 0.8 kg DM of a heat treated soybean meal (TSBM; DM = 24%, CP = 16%, aNDFom = 42%) and PRG plus 3.1 kg DM of a mix of citrus and heat treated soybean meal (Mix; DM = 32%, CP = 15%, aNDFom = 39%). The trial consisted of a 2-wk covariate period and 10 wk of data collection. Individual cow pasture DMI was obtained on wk 6 utilizing the n-alkane technique. Cattle were milked at 0730 h and 1600 h daily and milk yields recorded. Milk fat, protein and lactose concentrations were determined weekly from one successive PM and AM milking sample from each cow. All data were analyzed using the Proc Mixed procedure in SAS. Total DMI was greater for Citrus than PRG treatment and milk solid production was greater for TSBM and Mix treatments in comparison to PRG (Table 1). The results suggest metabolizable protein was first limiting milk solid production. Table 1 (Abstr. 412). Effects of supplemental concentrate type on DMI and milk production of mid-lactation dairy cattle grazing perennial ryegrass-based pasture¹

Item	PRG	Citrus	TSBM	Mix	SEM
Pasture intake (kg DM d⁻¹)	15.6^a	12.8^b	15.3^ac	13.8^bc	0.47
Supplement intake (kg DM d⁻¹)	0^a	4.8^b	0.8^c	3.1^d	0.03
Total intake (kg DM d⁻¹)	15.6^a	17.6^b	16.1^ab	16.9^ab	0.48
Milk production (kg d⁻¹)	18.5^a	20.6^b	20.3^b	21.3^b	0.34
Milk solids production (kg d⁻¹)	1.41^a	1.49^ab	1.55^b	1.59^b	0.03

^a–dDifferent superscripts within a row for a given treatment signifies P < 0.05. ¹PRG = perennial ryegrass, Citrus = perennial ryegrass + citrus pulp + urea, TSBM = perennial ryegrass + heat-treated soybean meal, Mix = perennial ryegrass + citrus pulp + heat-treated soybean meal.

Key Words: milk production, metabolizable protein, first limiting