Nitrogen use efficiency, reticulo-ruminal pH and behaviour of lactating cows grazing either in a full-time system or in a part-time system with indoor feeding of fresh herbage and concentrate

Abstract

Increasing herd size and fragmented or non-uniform land challenge pasture-based milk production systems. Therefore, part-time grazing combined with indoor feeding of fresh herbage (‘cut-and-carry’) allows to maintain the advantages of fresh-herbage-based diets. However, consequences for environmental nitrogen losses, animal behaviour and ruminal metabolism are decisive for its implementation. Animal performance, nitrogen use efficiency (NUE), reticulo-ruminal pH and feeding/locomotive behaviour were compared in six cows subjected either to full-time grazing (system F) or to part-time grazing system with indoor feeding of fresh herbage and concentrate (system P). Biweekly samplings were performed on six lactating cows per treatment in spring, summer and autumn. Nitrogen (N) balance was calculated from estimated N intake and N output via faeces, urine and milk. Reticulo-ruminal pH was recorded using a wireless data recorder. Eating and locomotive behaviour were measured with noseband sensors and pedometers. In spring, but not later, herbage intake per unit of body weight was higher for system F compared to system P cows. Eating time was shorter by 15% in P compared to F cows. Across systems, NUE declined from spring to summer/autumn from about 300 to 200 g milk protein N/kg N intake. Reticulo-ruminal pH was more variable under part-time grazing conditions, with a pronounced decrease subsequent to offering the herbage indoors. The part-time grazing system resulted in similar or higher NUE than full-time grazing. Additional studies with larger numbers of experimental units are required to be able to develop comprehensive recommendations for the improvement of the two grazing systems.

Effects of full-time v. part-time grazing on seasonal changes in milk coagulation properties and fatty acid composition

“…Details on botanical analysis and composition of pastures and leys are given in Akert et al . (2020). Cows were milked twice daily.…”

“…In IF, concentrate was provided only in spring making up 22 g/kg of dietary dry matter (DM). Details on concentrate composition used are given in Akert et al (2020).…”

“…Grazing heights were assessed daily with a rising plate meter and reached an average over all periods of 5.6, 7.7 and 8.1 cm for FG, IF and IFplus, respectively. Details on botanical analysis and composition of pastures and leys are given in Akert et al (2020). Cows were milked twice daily.…”

“…Energy-rich or balanced concentrates can reduce the dietary protein excess and thus result in lower milk urea contents. The lower milk urea content in the part-time grazing systems also reflects the lower crude protein content in grass fed indoors compared to the pasture grass (<180 v. >220 g/kg DM; reported in Akert et al, 2020). Total FA content in grass was highest in spring (19.1 and 16.9 g/kg dry matter (DM) in pasture and indoor grass respectively) and lowest in summer (15.1 and 13.3 g/kg DM in pasture and indoor grass respectively; online Supplementary Table S1).…”

“…In spring, for FG, IF and IFplus cows the energy balance calculated from body weight, milk yield and estimated grass intake using the double alkane method (cf. Akert et al, 2020) was −8.4, 6.4 and −15.6 MJ net energy for lactation per day, respectively. Various factors seem to affect milk FA composition of grass-fed cows in addition to grass proportion in diet or concentrate composition.…”