Influence of dietary phosphorus on the performance of lactating dairy cattle

Abstract

S U M M A R YIn an experiment, carried out over 3 years, two groups of dairy cows offered ad libitum access to grass silage received 8 kg/day concentrate differing only in phosphorus content (low P concentrate: 4 0 -4-5 g/kg dry matter (D.M.); high P concentrate: 60-6-5 g/kg D.M.) during the winter feeding period of approximately 6 months. During the summer period all animals were grazed together on perennial ryegrass pastures. There were no consistent significant effects of P content on any of the variables measured. The mean calving indices were 371 (S.E. = 3-71, n = 122) and 379 (S.E. = 4-28, n = 95) days and overall conception rates were 0-70 and 0-68 for the low and high P treatments, respectively. Mean plasma P concentrations during the winter period were significantly reduced (P < 001 or greater) in years 2 and 3 of the study on the low P treatment. In 1 year milk yield was significantly higher (P < 001) on the low P treatment although the fat content was significantly reduced (P < 005) but these effects were not recorded in the other 2 years. e s t ' m a t e s f°r sheep were reduced from 43-5 mg (ARC, 1965) to 140 mg P/kg live weight (LW) per The Technical Review of the nutrient requirements of day. The estimates for cattle were reduced from farm livestock by the Agricultural Research Council between 12 and 28 mg to 12 mg P/kg LW per day. (1965), contained estimates of the requirements of More recent information (Braithwaite, 1984) sugvarious classes of livestock for essential minerals.

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

“…While Valk and Sě bek (1999) observed no reduction in milk output in a study involving a dietary P level of 2.8 g P/kg DM, this study was conducted over 1.5 lactations, and excluded the early lactation period in year 1. In agreement with the findings of the current study, there is no evidence of a reduction in milk output in studies involving dietary P levels in excess of 3.3 g/kg DM (Table 1), although all but one of these studies (Brodison et al, 1989) were of less than 2 years in duration. Although it is likely that dietary P impacts on milk yield through a reduction in food intake, Valk and Sěbek (1999) observed that the fall in milk yield preceded the decline Diet had no significant effect on any of the milk composition parameters examined in the current study, although the effect of dietary P on milk composition in previous studies has been variable.…”

“…In addition, there was a trend for plasma P concentrations to decline with increasing lactation number, as observed by Forar et al (1982). Reduced plasma P concentrations have frequently been observed with cows offered 'low' P diets (Brodison et al, 1989;Dhiman et al, 1995;Wu et al, 2000;Lopez et al, 2004), although blood P concentrations do not necessarily provide a good indicator of P deficiency in ruminants (Forar et al, 1982). For example, plasma P concentrations are influenced by a range of factors (exercise, excitement, time of sampling, time of feeding, time of year, age and site of sampling) as reviewed by Beighle et al (1993).…”

“…This is of particular concern as the availability of P from different feedstuffs (concentrates, maize silage, alfalfa silage, grazed grass) may vary, while the availability of P from many feeds still does not appear to have been defined with certainty (NRC, 2001). Low P diets have been examined previously in grassland-based systems (Brodison et al, 1989), although this study involved relatively low-yielding dairy cows (5000 l per cow per lactation) that are not representative of those in most dairy herds today.…”

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

“…In more recent controlled studies (e.g. Call et al, 1987;Brodison et al, 1989;Brintrup et al, 1993;Valk and Sěbek, 1999;Wu and Satter, 2000;Wu et al, 2000), fertility performance was largely unaffected by dietary P levels, although these studies were primarily designed to examine the impact of dietary P level on cow performance. While infertility was the primary reason for cows being culled in the current experiment (Ferris et al, 2009), none of the fertility parameters examined during lactations 1 to 4 was affected by dietary P level, in agreement Table 3 Effect of dietary phosphorus level, lactation number when bone was sampled, and day of lactation when bone was sampled, on the composition of cortical bone removed from rib cores Dietary phosphorus levels for dairy cows with the findings of the studies highlighted above.…”

“…For example, while Brodison et al (1989) sampled tail bones, Beighle (1999) and Wu et al (2001) surgically removed rib biopsies. However, Beighle (1999) removed cores using a trephine, while Wu et al (2001) removed 20 cm rib sections.…”