Effect of offering dairy cows diets differing in phosphorus concentration over four successive lactations: 1. Food intake, milk production, tissue changes and blood metabolites

Abstract

The loss of phosphates from dairy farms contributes to the eutrophication of waterways. Whilst reducing the phosphorus (P) content of dairy cow diets has the potential to help reduce phosphate losses, diets containing inadequate dietary P may have a negative effect on cow health and performance. To address this issue, 100 winter-calving Holstein-Friesian dairy cows were offered diets containing either 'high' or 'low' levels of dietary P. The experiment was conducted over a 4-year period, with 80 primiparous cows commencing the study in year 1, while a further 20 primiparous cows commenced the study in year 2. Rations offered during the winter comprised grass silage, maize silage (70 : 30 dry matter (DM) basis, approximately) and concentrates (10.0 to 12.0 kg/cow per day). During the summer periods in years 1 and 2, half of the cows grazed both day and night, while the remaining cows grazed by day, and were housed by night and offered grass silage. During years 3 and 4, all cows grazed both day and night during the summer period. Concentrate feed levels during the summer periods were 3.0 to 4.0 kg/cow per day. Different dietary P levels were achieved by offering concentrates containing either high or low P levels during the winter period (approximately 7.0 or 4.4 g P/kg DM respectively), and during the summer period (approximately 6.8 or 3.6 g P/kg DM, respectively). Total ration P levels averaged 4.9 and 3.6 g P/kg DM for the 'high' and 'low' P winter diets respectively, and 4.2 and 3.6 g P/kg DM for the 'high' and 'low' P summer diets respectively. A total of 95, 70, 50 and 22 cows completed each of lactations 1 to 4 respectively. Dietary P level had no significant effect on food intake, milk output or milk composition ( P . 0.05). Plasma P concentrations were significantly lower with cows offered the 'low' P diet in each of lactations 1 to 4 ( P , 0.05). In each of lactations 3 and 4, cows offered the 'low' P diet tended to have lower condition scores and live weights than those offered the 'high' P diet. The results of this experiment highlight that the P content of dairy cow diets can be substantially reduced with no detrimental effect on dairy cow performance.Keywords: dairy cows, phosphorus, food intake, milk, blood Implications Phosphorus (P) of agricultural origin (primarily from fertiliser and feeds) contributes to eutrophication of waterways. A 4-year experiment was conducted to examine the longterm impact of reducing the P content of dairy cow concentrates on cow performance. Neither food intake, milk production or cow fertility were affected when dietary P levels were reduced by approximately 25% over this 4-year period. Reducing the P content of dairy cow diets has the potential to reduce P loss to the environment.

Effect of offering dairy cows diets differing in phosphorus concentration over four successive lactations: 2. Health, fertility, bone phosphorus reserves and nutrient utilisation

“…This study examines the effect of dietary P level on dairy cow health and fertility, bone composition and nutrient utilisation. In addition, the implications of the findings presented by Ferris et al (2009), and the results presented within this study, are considered in relation to rationing P for dairy cows, and in particular the most recent Agricultural and Food Research Council (AFRC) recommendations (1991).…”

“…The companion study (Ferris et al, 2009) describes a 4-year experiment in which 100 primiparous winter-calving HolsteinFriesian dairy cows were used to examine the impact of dietary P level on cow performance. Primiparous cows were allocated to either 'high' or 'low' P diets (50 cows per treatment) within 36 h of calving, with cows remaining on the same P treatment throughout the experiment.…”

“…Each year comprised a winter period, a grazing period, a late lactation period and a dry period. Full details of the diets offered, the management regimes imposed and the effect of diet on feed intake, milk production, tissue changes and blood metabolites have been presented by Ferris et al (2009). This study examines the effect of dietary P level on dairy cow health and fertility, bone composition and nutrient utilisation.…”

“…More recently, in a study involving grassland-based systems of milk production, Ferris et al (2009) observed that food intake and milk output was unaffected when the P content of dairy cow diets was reduced over a 4-year period by proportionally 0.27 (from 4.9 to 3.6 g/kg dry matter (DM), approximately) during the winter, and by proportionally 0.17 (from 4.2 to 3.6 g/kg DM, approximately) during the summer. The long-term nature of this study was necessary as dairy cows can mobilise bone P reserves, especially in early lactation.…”

“…This study examines the long-term effects of offering the diets described by Ferris et al (2009) on dairy cow health, fertility and bone composition and on nutrient utilisation.…”