A proposed new approach and protocol to defining mineral deficiencies using reference curves. Cobalt deficiency in young sheep is used as a model

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.

Major trace elements limiting livestock performance in New Zealand

Abstract Extract • Many New Zealand soils are naturally deficient in cobalt and/or selenium and/or copper, or are naturally high in molybdenum. livestock granng pasture grown on such soils may be deficient in one or more of these trace elements. • In the 1940s and 1950s, New Zealand researchers were at the forefront of research to define the cause of trace-element related ill-thrift and clinical diseases like white muscle disease, peat scours and enzootic ataxia. • New Zealanders have devised production-related reference ranges for blood and liver copper, vitamin B(12) and selenium that are used for the diagnosis and prevention of deficiencies. • A range of supplementation procedures has been devised, from topdressing or spraying pasture to direct animal supplementation, to suit the range of livestock management systems found in New Zealand. • Trace-element monitoring programmes are now a routine procedure for farmers grazing cattle, sheep, and deer on trace-element deficient land. • Copper deficiency is the main trace-element deficiency diagnosed in deer.

A review of tissue reference values used to assess the trace element status of farmed red deer (Cervus elaphus)

AIMS

This paper reviews the principles for the establishment of biochemical reference criteria for assessing the trace element status of farmed livestock and summarises data for copper, selenium, vitamin B12 and iodine for farmed red deer.

COPPER

Enzootic ataxia and osteochondrosis occur when liver copper concentrations are below 60 micromol/kg fresh tissue, and serum copper concentrations are below 3-4 micromol/l. Growth responses to copper supplementation have been equivocal when blood copper concentrations were 3-4 micromol/l, but were significant when mean blood copper concentrations were 0.9-4.0 micromol/l. No antler growth or bodyweight response to copper supplementation was observed when blood ferroxidase levels averaged 10-23 IU/l (equivalent to serum copper concentrations of 6-13 micromol/l) and liver copper concentrations averaged 98 mumol/kg fresh tissue. These data suggest that 'deficient', 'marginal' and 'adequate' ranges for serum copper concentrations should be 5, 5-8, and 8 micromol/l, respectively, and those for liver copper concentrations should be 60, 60-100, and 100 micromol/kg, respectively.

SELENIUM

White muscle disease has been reported in young deer with blood and liver selenium concentrations of 84-140 nmol/l and 240-500 nmol/kg fresh tissue, respectively. No growth-rate response to selenium supplementation occurred in rising 1-year-old deer when blood selenium concentrations were less than 130 nmol/l, the range in which a growth-rate response would be expected in sheep. VITAMIN B12: Vitamin B12 concentrations in deer are frequently below 185 pmol/l without clinical or subclinical effects. No growth response was observed in young deer with vitamin B12 concentrations as low as 75-83 pmol/l. A growth response to cobalt/vitamin B12 supplementation occurs in lambs with serum vitamin B12 concentrations 336 pmol/l.

CONCLUSIONS

Data that can be used to establish reference ranges for assessing trace element status in deer are limited. More robust reference values for farmed red deer need to be established through further studies relating biochemical data to health and performance.

A review of selenium deficiency in grazing ruminants Part 2: Towards a more rational approach to diagnosis and prevention

ESTIMATING SELENIUM STATUS: Although the importance of selenium in ruminants has been recognised for over 30 years, problems associated with selenium deficiency are still frequently identified in grazing livestock operations. There is a growing diversity of tools available for the management of selenium deficiency giving rise to diagnostic and therapeutic dilemmas for the veterinary practitioner. There is no single test for selenium adequacy which can be considered superior in all diagnostic situations because the method of choice depends on the objective of the testing procedure.

REFERENCE RANGES

Reviewing the available data, the current New Zealand reference ranges for selenium concentrations in ruminant tissue and feed appear valid.

CLINICAL RELEVANCE

Management of selenium deficiency will continue to be important in grazing ruminants. Practising veterinarians should be familiar with the appropriate use of tests for selenium deficiency. Advice should be based on micronutrient analysis of animal tissue, defensible reference ranges backed by production response data, and supplementation programmes which optimise the return on investment.