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...

Prenatal growth is sensitive to the direct and indirect effects of maternal dietary intake; manipulation can lead to behavioural and physiological changes of the offspring later in life. Here, we report on three aspects of how a high-salt diet during pregnancy (conception to parturition) may affect the offspring's response to high oral salt loads: (i) dietary preferences for salt; (ii) response to salt and water balance and aldosterone and arginine vasopressin (AVP) concentrations after an oral salt challenge; (iii) concentrations of insulin and leptin after an oral salt challenge. We used two groups of lambs born to ewes fed either a high-salt (13% NaCl) diet during pregnancy (S lambs; n 5 12) or control animals born to ewes fed a conventional (0.5% NaCl) diet during pregnancy (C lambs; n 5 12). Lambs were subjected to short-(5 min) and long-term (24 h) preference tests for a high-salt (13% NaCl) or control diet, and the response to an oral challenge with either water or 25% NaCl solution were also carried out. Weaned lambs born to ewes fed high salt during pregnancy did not differ in their preference for dietary salt, but they did differ in their physiological responses to an oral salt challenge. Results indicate that these differences reflect an alteration in the regulation of water and salt balance as the metabolic hormones, insulin and leptin, were not affected. During the first 2 h after a single salt dose, S lambs had a 25% lower water intake compared to the C lambs. S lambs had, on average, a 13% lower AVP concentration than the C lambs (P 5 0.014). The plasma concentration of aldosterone was higher in the S lambs than in the C lambs (P 5 0.013). Results suggest that lambs born to ewes that ingest high amounts of salt during pregnancy are programmed to have an altered thirst threshold, and blunted response in aldosterone to oral salt loads.

Producers have the possibility to combat human-induced dryland salinity by planting salt-tolerant plants such as saltbush. Saltbush has the potential to be used as a source of food for livestock at a time and place where pasture is not viable. However, saltbush contains high concentrations of sodium chloride salt and some other anti-nutritional factors that have the potential to affect feed and water intake and, directly or indirectly, the reproductive capacity of sheep. High-salt diet during gestation induces a small modification of the activity of the renin-angiotensin system (RAS) that has an important role in the maintenance of the salt-water balance in non-pregnant and pregnant sheep. In contrast, the main effect of salt ingestion during pregnancy is observed on the biology of the offspring, with changes in the response of the RAS to salt ingestion and altered thirst threshold in response to an oral salt ingestion. These changes, observed later in life, are the result of fetal programming following the ingestion of salt by the mother. It seems that the exposure to salt during pregnancy could provide an advantage to the offspring because of this adaptive response. The response may be particularly useful, for example, when grazing herbivores are fed halophytic forages adapted to saline soils.