The effects of supplementary phosphorus on the voluntary consumption and digestibility of a low phosphorus straw-based diet given to beef cows during pregnancy and early lactation

Abstract

Two similar experiments were conducted in consecutive years using a total of 26 pregnant beef cows. The two groups of 13 cows were given 2 kg molassed sugar-beet pulp (SBP)/day for the last 16 weeks of pregnancy and 3 kg SBP/day for the first 6 weeks of lactation with oat straw ad libitum. One group was given 250 g of a fully soluble liquid supplement (LS) containing urea, phosphoric acid, calcium and sodium chloride, trace elements and vitamins poured on to the SBP. The other group received no supplementary phosphorus but was given the same amounts of supplementary nitrogen (as crystalline urea) and calcium (as calcium carbonate) together with the same amounts of sodium chloride, trace elements and vitamins as were present in the LS. The LS provided 3-7 g P/day. The overall mean phosphorus intakes of the two groups were about 5-5 g (unsupplemented) and 10-5 g P (LS)/day. During pregnancy, reduced phosphorus intakes did not affect either the voluntary intake or digestibility of the straw. There was, however, a reduction in the blood phosphorus concentration for the cows which did not receive LS.After calving, the voluntary straw intake, digestibility of straw organic matter, metabolizablo energy intakes and blood phosphorus concentrations of the cows which received no phosphorus supplement were severely reduced. Using the present data and that from an earlier, similar experiment, a highly significant relationship was established between blood phosphorus concentration and voluntary straw intake during the period 5-6 weeks after calving for those cows with a blood phosphorus concentration below 1-0 mmol P/l. This relationship was voluntary straw intake (kg D.M./day) = 1-55 + 5-01 x blood phosphorus concentration (mmol/1).These results, obtained with individually fed, housed cattle, tend to suggest that a total phosphorus intake of only about 10-12 g P/day (of which 3-7 g was in the form of phosphoric acid) was adequate to maintain normal blood phosphorus concentration and voluntary straw intake and digestibility by these beef cows over the last 16 weeks of pregnancy and the first 6 weeks of lactation. This should be contrasted with the results of a similar experiment conducted earlier which clearly indicated that a daily intake of about 12 g P/day derived solely from sugar-beet pulp and oat straw was markedly inadequate. major consequence of severe dietary phosphorus inadequacy is a reduced voluntary intake of The recommended daily minimum intakes of fibrous roughages (e.g. straw) and an accompanying phosphorus for 500 kg cows in late pregnancy and reduction in the digestibility of the dry matter in early lactation (7-5 kg milk/day) given by the (D.M.) consumed. In the short term (3 weeks Agricultural Research Council (1965) of 34 and feeding) in late pregnancy, 400 kg cows given a 38 g P have been reduced to 17 and 23 g P respec-low-phosphorus diet composed of molassed sugartively (Agricultural Research Council, 1980). A beet pulp and oat straw (6g P/day) had similar

Straw yields and nutrients of seventy-five Canadian barley cultivars

“…However, barley straw normally does not meet the protein, Mg, Mn (Mathison et al 1981), and P (Bass et al 1981) requirements of cattle diets. Chemical and microbiological processes can improve the nutritive value of straw but these are costly, and chemical methods can increase the risk of environmental pollution (Kelley 1992).…”

Dietary nitrogen and phosphorus depletion in cattle and their effects on liveweight gain, blood metabolite concentrations and phosphorus kinetics

“…A legumes, especially Stylosanthes spp. which tolerate deficiency of either nutrient will cause a reduction in low P soils, have been undertaken to improve the dry feed intake and liveweight change in both cattle and season protein nutrition of Australian grazing cattle, sheep (Campling et al 1962;Egan 1965;Little 1968; These legumes are frequently high in dietary N and Bass et al 1981;McMeniman 1990;Ternouth & calcium but low in P (Gilbert et al 1989 a, b;Coates Sevilla 1990). Owing to the low P content of the soils and the Very few detailed investigations have been conseasonality of pasture production and quality ducted to determine the effects of combined dietary N (Lemerle el al.…”

A note on the effects of dietary protein degradability in the rumen on the voluntary intake and digestibility of barley straw by lactating beef cows

“…The mean data from six previous similarly conducted experiments at this unit, involving dietary treatments with urea with either about 3 kg barley or molassed sugar-beet pulp plus ad libitum oat straw (with four to 16 cows per treatment) (Fishwick, Fraser, Hemingway, Parkins and Ritchie, 1977a;Fishwick, Fraser, Hemingway, Parkins and Ritchie, 1977b;Bass, Fishwick, Hemingway, Parkins and Ritchie, 1981;G. Fishwick, personal communication, 1985) were also tested for the relationship between voluntary straw consumption and RDP supplied.…”