The effect of a change in blood acid-base status on body composition and mineral retention in growing lambs

Abstract

Three groups of lambs of about 25 kg live weight were given a concentrate diet either on its own (eight lambs) or supplemented with 10 g/kg ammonium chloride (eight lambs) or 20 g/kg sodium bicarbonate (12 lambs). At about 45 kg live weight the lambs were killed and their body composition was determined. The composition of their gains was also determined using information obtained from a fourth group of lambs (eight lambs) which were killed at the start of the experiment. Lambs given the ammonium chloride diet showed a reduction in blood pH while those given the sodium bicarbonate diet showed an increase to levels seen in lambs given forage diets. There were also marked effects on calcium (Ca), phosphorus (P) and magnesium retention with retentions being reduced in those given the ammonium chloride diet and increased in" those given the bicarbonate diet. The average rates of retention of Ca and P in lambs given the bicarbonate diet were 9-1 and 5-9 g/kg empty-body weight gain and are comparable with rates seen in lambs given forage diets. These results suggest that dietary induced changes in blood acid-base status is a major factor contributing to the lower rates of retentions of these minerals in lambs given cereal-based diets.

The effects of feeding diets containing either NaHCO3 or NH4Cl on indices of bone formation and resorption and on mineral balance in the lamb

“…These results confirm earlier studies in which a diet-induced fall in blood pH led to a similar decrease in mineral retention in growing lambs (Abu Damir et al 1990 Chronic metabolic acidosis has been shown to cause a decline in the conversion of 25-hydroxyvitamin D3 (25(OH)D3) to 1,25(OH)2 D3 due to reduced renal 25(OH)D3-1-hydroxylase activity in both rats and chicks fed low-Ca diets (Lee et al 1977;Kawashima et al 1982;Ro et al 1990). A reduction in 1,25(OH)2D3 production might be expected to lead to a fall in intestinal Ca absorption and it was originally thought that this might offer an explanation for the lower rates of mineral retention seen in lambs fed the acid diet.…”

“…Similar differences in mineral retention have also been seen in lambs fed diets containing either NH4C1 or NaHCO3 and point to diet-induced changes in blood acid-base status as being an important factor affecting mineral retention in the lamb (Abu Damir, Scott, Thompson, Topps, Buchan & Pennie, 1990). To date we have no information as to the mechanism leading to this change in retention, though studies in other species suggest that a number of factors may be involved.…”

Effects of acute acid loading on parathyroid hormone secretion and on urinary calcium and cAMP excretion in the growing lamb

“…In summary, these results point to the kidney as the initial site of response to acid loading in the lamb; an increase in urine Ca loss necessitating an increase in PTH secretion and an increase in bone resorption in order to maintain normal plasma Ca levels; this effect of acidosis on the kidney being directly responsible for the lower rates of mineral retention seen previously in lambs fed acid diets (Abu Damir et al 1990.…”

“…Lambs fed concentrate diets based on cereals such as maize or barley together with a protein source such as fish or soya bean meal have been shown to retain Ca and P at lower rates than those fed forage diets (Thompson, Gelman & Weddell, 1988; Wan Zahari, Thompson, Scott & Buchan, 1989). Previously, we suggested that this might be due to dietary-induced differences in their blood acid-base status, lambs fed concentrate diets being mildly acidotic whereas those fed forage diets are slightly alkalotic (Abu Damir, Scott, Thompson, Topps, Buchan & Pennie, 1990). To test this, we fed lambs a diet supplemented with either NH4Cl or NaHCO3 to adjust their blood acid-base status to levels seen in lambs fed either concentrate or forage diets, and showed that this had similar effects on Ca and P retention as found in lambs fed such diets (Abu Damir et al 1990).…”

Aspectos clínicos e laboratoriais em ovinos submetidos a dietas com níveis elevados de enxofre com objetivo de indução de polioencefalomalácia

“…Nos 12 momentos aferidos, tanto o pH sanguíneo quanto o pH ruminal mantiveram-se dentro dos valores de referência considerados normais para a espécie (Radostits et al 2007). Neste trabalho, além da substituição gradativa do feno pela ração (fase 2), havia 2% bicarbonato de sódio na dieta o que, segundo Damir et al (1990) Grupos: G1 = 0,2% enxofre M; G2 = 0,9% enxofre MS; G3 = 1,2% enxofre MS. M1: 1º dia da fase de adaptação. M12 = 90º dia da fase 3 (fornecimento dieta com 95% da ração experimental e 5% de feno).…”