Free-choice consumption of mineral lick blocks by fattening lambs fed ad libitum alfalfa hay and concentrates with different trace mineral content

Trace Mineral Feeding and Assessment

Trace minerals are commonly supplemented in ruminant feeds as many common feeds are deficient in one or more of the trace minerals. The requirement of trace minerals needed to prevent classic nutrient deficiencies is well established, thus those cases most commonly occur when no supplement is provided. The more common challenge for the practitioner is to determine if additional supplementation is needed to enhance production or decrease disease occurrence.

The effects of offering mineral blocks to ewes pre-mating and in late pregnancy on block intake, pregnant ewe performance and immunoglobulin status of the progeny

Two experiments were carried out to quantify the intake of mineral blocks by ewes in group- and individually fed situations, and to examine the effects of mineral block intake on food and water intake, colostrum production and lambs' immunoglobulin G (IgG) absorption when ewes are individually housed and offered maize or grass silage with a concentrate supplement. In experiment 1, mineral blocks were offered to 359 ewes either when grazing at mating time (no. = 200) or, when indoors in the last 4 or 7 weeks of pregnancy, the latter as either twin-bearing ewes that were group-fed (no. = 18) or individually fed (no. = 27) or single-bearing ewes that were group-fed (no. = 114). Block intake was measured on a weekly basis. In experiment 2,a2X2 X 2 factorial design was used to compare the effects of forage (grass or maize silage), restricted mineral block access and added minerals/vitamins in the concentrate on food and water intakes, colostrum production and immunoglobulin absorption by the lamb using 64 twin- bearing ewes that were individually housed. Grass silage and maize silage were offered ad libitum, concentrates were offered at a flat rate of 400 g per head per day. Mineral blocks were offered to ewes for 3 h/day. Following lambing, the ewes were hand milked at 1,10 and 18 h post partum. Colostrum samples were assayed for immunoglobulin G (IgG) content. Lambs were blood sampled at 24 h old to determine serum IgG value. In experiment 1, mean daily mineral block intake per ewe was lowest at mating time (19 g) and highest when ewes were individually housed (194 g). In experiment 2, intakes of dry matter(DM) and energy were higher (F < 0.05) in the maize silage treatments. Similarly, when ewes had access to mineral blocks they had higher (P < 0.05) intakes of DM, energy and protein in addition to having a higher water intake (2.24 v. 0.771 per ewe per day; s.e. 0.139; P < 0.01). The mean total colostrum yield to 18 h post lambing at 1734 ±98.0 ml was unaffected by any of the treatments. When ewes had access to mineral blocks their lambs had lower (6.8 v. 18.8; s.e. 1.48; P < 0.01) serum IgG values and the efficiency of IgG absorption from the colostrum into the blood stream was reduced (0.097 v. 0.247; s.e. 0.0214; P < 0.01). In conclusion, the data show that there is wide variation in mineral block intake in different situations and that intake of some minerals can exceed toxic values. Additionally, when individually fed pregnant ewes have access to blocks for just 3 h/day, there is a significant increase in water intake and a dramatic reduction in lamb serum IgG concentration and in the efficiency of absorption of colostral IgG into the blood. We suggest that while mineral blocks can confer advantages in specific situations, there is the need to revisit their formulation and to further research the mode of action responsible for the compromised IgG absorption.

The effect of varying levels of mineral and iodine supplementation to ewes during late pregnancy on serum immunoglobulin G concentrations in their progeny

Three experiments were carried out to evaluate the effects of varying levels of mineral and iodine supplements when offered to ewes in late pregnancy on lamb serum immunoglobulin G (IgG) concentrations. In experiment 1, 44 individually housed ewes were allocated to one of four treatments (no. = 11) and offered a basal diet of grass silage ad libitum which was supplemented with 500 g/day of a concentrate (190 g/kg of crude protein (CP)), in addition to mineral/vitamin fortification at the rate of 0 g (C), 17.3 g (LM), 34.6 g (MM) or 52.0 g (HM) per day for the final 7 weeks of pregnancy. The mineral/vitamin supplement contained Ca, P, Na, Mg, Mn, Se, I, Co, Mn and vitamin E. The ewes were milked at 1 h, 10 h and 18 h post partum and measured quantities of colostrum, proportional to lamb birth weight, were fed back to the lambs via a stomach tube. Treatment had no effect on total colostrum yield or total IgG yield to 18 h post partum (P > 0.05). There was a linear decrease in serum IgG concentration and IgG absorption efficiency as mineral supplementation increased (P < 0.001). In experiment 2, which was carried out in conjunction with experiment 1, 44 ewes were allocated to four treatments (no. = 11) and offered the same basal silage/concentrate diet as in experiment 1, in addition to receiving one of the following supplements : (C) control, as in experiment 1; (HM), as in experiment 1; (−I), ewes offered the same mineral/vitamin supplement as HM but with iodine excluded; (I0), ewes offered a daily mineral supplement of iodine only at a level of 40 mg per ewe, equivalent to the iodine inclusion in the 52 g of minerals offered in HM. The iodine-supplemented progeny (HM and IO) had lower (P < 0.001) serum IgG concentrations and higher soil scores (P < 0.05) than the C and −I progeny. In experiment 3, the effects of varying levels of iodine supplementation when offered to ewes during the final 6 weeks of pregnancy on lamb serum IgG values were examined. Forty-eight individually housed ewes were allocated to one of four treatments (no. = 12) and offered grass silage ad libitum, which was supplemented initially with 500 g of a concentrate (140 g/kg of CP) from days 99 to 130 of gestation and then replaced with 700 g/day of a concentrate (180 g/kg of CP) from day 131 of gestation until lambing. In addition, the diet of each ewe was supplemented on a daily basis with iodine at the rate of 0 mg (C), 8.9 mg (LI), 17.7 mg (MI) or 26.6 mg (HI). There was a negative linear reduction in serum IgG concentration and IgG absorption efficiency as maternal dietary iodine supplementation increased (P < 0.001). We conclude that supplementation of the ewe's diet in late pregnancy with 17.3 g of a mineral supplement as formulated in the current experiment lowers the lamb's ability to absorb colostral IgG, and offering only the iodine component of this mineral supplement, at a level which approximates to about one third of currently quoted toxicity levels, will result in reduced serum IgG concentration in the lamb. These findings suggest the need to re-examine current toxicity values for iodine.