Reproductive capacity of Merino ewes fed a high-salt diet

Abstract

An option to increase the productivity of saline land is to graze sheep on salt-tolerant plants, which, during the summer/ autumn period, can contain 20% to 25% of their dry matter as salt. This study assessed the impact of coping with high dietary salt loads on the reproductive performance of grazing ewes. From the time of artificial insemination until parturition, 2-year-old maiden Merino ewes were fed either a high-salt diet (NaCl 13% of dry matter) or control diet (NaCl 0.5% of dry matter). Pregnancy rates, lamb birth weights, milk composition and the plasma concentrations of hormones related to salt and water balance, and energy metabolism were measured. Leptin and insulin concentrations were lower (1.4 6 0.09 v. 1.5 6 0.12 ng/ml; (P , 0.05) and 7.2 6 0.55 v. 8.2 6 0.83 ng/ml; P , 0.02) in response to high-salt ingestion as was aldosterone concentration (27 6 2.7 v. 49 6 5.4 pg/ml; P , 0.05), presumably to achieve salt and water homeostasis. Arginine vasopressin concentration was not significantly affected by the diets, but plasma concentration of T 3 differed during gestation (P , 0.02), resulting in lower concentrations in the high-salt group in the first third of gestation (1.2 6 0.18 v. 1.3 6 0.14 pmol/ml) and higher concentrations in the final third of gestation (0.8 6 0.16 v. 0.6 6 0.06 pmol/ml). T 4 concentration was lower in ewes ingesting high salt for the first two-thirds of pregnancy (162 6 8.6 v. 212 6 13 ng/ml; P , 0.001). No substantial effects of high salt ingestion on pregnancy rates, lamb birth weights or milk composition were detected.Keywords: aldosterone, high salt, insulin, leptin, reproduction IntroductionSalinity is an increasing problem in agriculture worldwide (Ghassemi et al., 1995) and the use of halophytic plants such as saltbush represents one of the few options available to revegetate salinised landscapes and re-establish grazing systems . Some landholders in Australia are grazing sheep on saltbush to fill a summer/ autumn feed gap (Masters et al., 2006), a period that coincides with the greater demands of late pregnancy for autumn-or winter-lambing ewes. However, feeding saltbush may possibly have a negative impact on reproductive performance of the ewes as high salt intake may reduce intake and cause physiological changes associated with adaptation to the salt load.High salt intake has been shown to reduce voluntary feed intake (Masters et al., 2005;Blache et al., 2007) as well as the efficiency of energy use for production (Arieli et al., 1989) in sheep. A decrease either in voluntary feed intake or in fat reserves is usually associated with a decrease in the concentration of metabolic hormones such as insulin and leptin (Chilliard et al., 2005) and recently a high salt ingestion has been shown by Blache et al. (2007) to affect energy metabolism through changes in insulin concentrations in sheep fed high salt (20% NaCl) diets. Thus, the ingestion of large amount of salt may impact energy availability and consequently reproductive performance.There are also physiological 'con...

Salt intake and reproductive function in sheep

“…Similarly, in a recent study, feeding pregnant ewes with high-salt diets (lupin and barley grain, 13% NaCl, 18.8 CP (% of DM; Digby et al, 2008) from the time of conception until parturition, did not compromise reproductive efficiency (Digby et al, 2008). Lambs born of ewes fed high-salt diet (13% NaCl) had a normal crown-to-rump length, birth weight and a similar survival rate as lambs born of ewes fed a diet containing typically standard levels of salt (0.5% NaCl; Digby et al, 2008). In addition, the high-salt diet was equally well tolerated during pregnancy in maiden ewes and multiparous ewes, regardless of the number of lambs borne (Digby et al, 2008;Chadwick et al, 2009a).…”

“…Lambs born of ewes fed high-salt diet (13% NaCl) had a normal crown-to-rump length, birth weight and a similar survival rate as lambs born of ewes fed a diet containing typically standard levels of salt (0.5% NaCl; Digby et al, 2008). In addition, the high-salt diet was equally well tolerated during pregnancy in maiden ewes and multiparous ewes, regardless of the number of lambs borne (Digby et al, 2008;Chadwick et al, 2009a).…”

“…Feeding of ewe lambs from weaning through pregnancy with diets containing sodium chloride (0.5% to 13.1%) had no major adverse effects on their growing and fattening performance or their breeding capacity (Meyer and Weir, 1954). Similarly, in a recent study, feeding pregnant ewes with high-salt diets (lupin and barley grain, 13% NaCl, 18.8 CP (% of DM; Digby et al, 2008) from the time of conception until parturition, did not compromise reproductive efficiency (Digby et al, 2008). Lambs born of ewes fed high-salt diet (13% NaCl) had a normal crown-to-rump length, birth weight and a similar survival rate as lambs born of ewes fed a diet containing typically standard levels of salt (0.5% NaCl; Digby et al, 2008).…”

“…The complex composition of saltbush makes the interpretation of results somewhat difficult when the plant is fed to sheep. A systematic approach aiming at understanding the role of sodium chloride salt in saltbush has been taken by different groups by developing a model in which sheep are fed a diet supplemented with salt (highsalt diet containing 5% to 20% NaCl; Meyer and Weir, 1954;Wilson, 1966c;Wilson and Hindley, 1968;Hemsley et al, 1975;Masters et al, 2005;Blache et al, 2007b;Digby et al, 2008;Chadwick et al, 2009aChadwick et al, , 2009bChadwick et al, and 2009c.…”

“…In contrast to pregnant ewes drinking saline water, pregnant ewes fed a high-salt diet during gestation can maintain their pregnancy, and the lambs are born within normal measures of weight and crown-to-rump length (Meyer and Weir, 1954;Digby et al, 2008;Chadwick et al, 2009a). Feeding of ewe lambs from weaning through pregnancy with diets containing sodium chloride (0.5% to 13.1%) had no major adverse effects on their growing and fattening performance or their breeding capacity (Meyer and Weir, 1954).…”