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This 2 × 2 factorial design experiment was conducted to compare the performance of spring-calving Holstein dairy cows (HOL, n = 34) with Swedish Red × Jersey/Holstein crossbred (SR × J/HOL, n = 34) dairy cows within low and medium concentrate input grassland-based dairy systems. The experiment commenced when cows calved and encompassed 1 full lactation. Cows were offered diets containing grass silage and concentrates [70:30 dry matter (DM) ratio, and 40:60 DM ratio, for low and medium, respectively] until turnout, grazed grass plus either 1.0 or 4.0 kg of concentrate/d during the grazing period (low and medium, respectively), and grass silage and concentrates (85:15 DM ratio, and 70:30 DM ratio, for low and medium, respectively) from rehousing and until drying off. No significant genotype × system interactions were present for any of the feed intake or full-lactation milk production data examined. Full-lactation concentrate DM intakes were 769 and 1,902 kg/cow for the low and medium systems, respectively, whereas HOL cows had a higher total DM intake than SR × J/HOL cows in early lactation, but not in late lactation. Although HOL cows had a higher lactation milk yield than SR × J/HOL cows, the latter produced milk with a higher fat and protein content, and thus fat plus protein yield was unaffected by genotype. Milk produced by the SR × J/HOL cows had a higher degree of saturation of fatty acids than milk produced by the HOL cows, and the somatic cell score of milk produced by the former was also higher. Throughout the lactation, HOL cows were on average 30 kg heavier than SR × J/HOL cows, whereas the SR × J/HOL cows had a higher body condition score than the HOL cows. Holstein cows had a higher incidence of mastitis and ovarian dysfunction that SR × J/HOL cows. [ABSTRACT FROM AUTHOR]

Abstract: This study determined in vitro rumen CH4 production of perennial ryegrass grown within a well managed Irish dairy production system. Four strategies, consisting of two pre-grazing herbage mass (HM; high ∼2400 and low ∼1600kg dry matter (DM)/ha) and two sward allowance (SA; high ∼20 and low ∼15kg DM/cow/d) treatments, were compared throughout the grazing season using an in vitro rumen gas production technique. Samples were collected during five 22 d sampling periods (SP 1–5) throughout the growing season and analysed for in vitro rumen CH4 output, and total gas and volatile fatty acid production following 24h of incubation with rumen fluid and artificial saliva. High HM was associated with lower organic matter digestibility and crude protein concentration compared with low HM, whereas SA had no effect on herbage composition. Methane output as ml/g DM incubated or digested was higher (P<0.05) for the high HM treatment than for the low HM treatment (25.5 versus 24.6 and 32.2 versus 30.5, respectively). Sward allowance had no effect on CH4 output, but CH4 output/g DM incubated or digested was affected by sampling period. Sward allowance did not alter methanogenesis and, although HM affected CH4 output in vitro, the biological scale of this effect was small. Thus, grass management strategy had little impact on in vitro rumen CH4 output when herbage was consistently of high nutritional quality. This article is part of the special issue entitled: Greenhouse Gases in Animal Agriculture – Finding a Balance between Food and Emissions, Guest Edited by T.A. McAllister, Section Guest Editors; K.A. Beauchemin, X. Hao, S. McGinn and Editor for Animal Feed Science and Technology, P.H. Robinson. [Copyright &y& Elsevier]

Abstract: In many in vitro studies feeds are dried in heated ovens with forced air ventilation and milled through a screen with 1mm apertures to obtain a physically representative small sample. Drying methods involving heat have been shown to change the chemical composition of feeds, and it is possible that changes in the chemical composition during thermal drying could affect in vitro rumen CH4 output measured on the samples. Hence, samples are often dried by freeze drying. The objective of this study was to compare effects of freeze drying at −55°C for 72h versus thermal drying at 40°C for 48h on the chemical composition and CH4 output of perennial ryegrass samples collected at 5 stages of primary growth (i.e., 12 May, 26 May, 9 June, 23 June, 7 July) using an in vitro rumen gas production technique. The magnitude of the changes in chemical composition due to drying method was small and not biologically important, and drying method had no effect on CH4 output. With advancing maturity at harvest, digestibility of the herbage declined. Methane output/g dry matter (DM) incubated decreased linearly while CH4 output/g DM digested increased linearly with advancing grass maturity. Thermal drying on a range of grass samples had a similar effect to freeze drying on in vitro rumen CH4 output, reflecting the small degree of change in chemical composition. This paper is part of the special issue entitled: Greenhouse Gases in Animal Agriculture – Finding a Balance between Food and Emissions, Guest Edited by T.A. McAllister, Section Guest Editors: K.A. Beauchemin, X. Hao, S. McGinn and Editor for Animal Feed Science and Technology, P.H. Robinson. [Copyright &y& Elsevier]