Sheep lactation

The results of metabolism studies with laboratory animals and livestock indicate that endosulfan does not bioconcentrate in fatty tissues and milk. Lactating sheep administered radiolabeled endosulfan produced milk containing less than 2% of the label. Endosulfan sulfate was the major metabolite in milk (Gorbach et al. 1968). A half-life of about 4 days was reported for endosulfan metabolites in milk from survivors of a dairy herd accidentally exposed to acutely toxic concentrations of endosulfan endosulfan sulfate accounted for the bulk of the residues detected in the milk (Braun and Lobb 1976). No endosulfan residues were detected in the fatty tissue of beef cattle grazed on endosulfan-treated pastures for 31-36 days (detection limits of 10 ppm for endosulfan, 40 ppm for endosulfan diol) the animals began grazing 7 days after treatment of the pastures. Some residues were detected in the fatty tissue of one animal administered 1.1 mg/kg/day of endosulfan in the diet for 60 days. No endosulfan residues were... 

High expression levels of proteins are potentially attained. In many instances, the level of expression exceeds 1 g protein/litre milk. In one case, initial expression levels of 60 g l-1 were observed, which stabilized at 35 g L1 as lactation continued (the expression of the arantitrypsin gene, under the influence of the ovine P-lactoglobulin promoter, in a transgenic sheep). Even at expression levels of 1 g L1, one transgenic goat would produce a similar quantity of product in 1 day as would be likely recoverable from a 50-1001 bioreactor system. 

Nitric oxide (NO) has also been implicated in certain maternal behaviors, including the timing of parturition in rats and olfactory memory formation in lactating sheep (Gammie and Nelson, 1999), as well as aggression and maternal aggression. Nitric oxide is produced from L-arginine by three different tissue-localized nitric oxide synthase (NOS) enzymes neuronal (nNOS), en-... 

Milk contains, on average, 0.03 mg thiamin per 100 g. Most (50-70%) of the thiamin in bovine milk is in the free form lesser amounts are phos-phorylated (18-45%) or protein-bound (7-17%). The concentration in mature human milk is somewhat lower (c. 0.02 mg per 100 g). Human colostrum contains only trace amounts of thiamin which increase during lactation. Pasteurized milk from goats and Channel Island breeds of cow contain about 0.04 mg per lOOg, while values for raw sheep s milk are somewhat higher, with an average of 0.08 mg per 100 g. Most of the thiamin... 

Milk contains about 0.1 mg niacin per 100 g and thus is not a rich source of the preformed vitamin. Tryptophan contributes roughly 0.7 mg NE per 100 g milk. In milk, niacin exists primarily as nicotinamide and its concentration does not appear to be affected greatly by breed of cow, feed, season or stage of lactation. Pasteurized goats (0.3 mg niacin and 0.7 mg NE from tryptophan per 100 g) and raw sheep s (0.4 mg niacin and 1.3 mg NE from tryptophan per 100 g) milk are somewhat richer than cows milk. Niacin levels in human milk are 0.2 mg niacin and 0.5 mg NE from tryptophan per 100 g. The concentration of niacin in most dairy products is low (Appendix 6A) but is compensated somewhat by tryptophan released on hydrolysis of the proteins. 

Cefazolin is a first-generation cephalosporin with antibacterial activity similar to that of penicillin G but it is -lactamase-resistant. It is poorly absorbed from the gastrointestinal tract and, thus, it is primarily administered parenterally. It is widely used for ticatment of mastitis in lactating cows, sheep, and goats and for treatment at drying off by the intramammary route. 

When tilmicosin was administered to six lactating cows as a single subcutaneous dosage of 10 mg/kg (104), residues in milk were higher than 25 ppb from 19 to 31 days postdosing. Following subcutaneous administration to sheep, a maximum concentration of 10247 ppb of tilmicosin was observed in milk at 8 h after dosing by day 12, however, the concentration of tilmicosin was below the MRL of 50 ppb. The half-life of tilmicosin in milk was calculated to be approximately 24 h (105). 

Enrofloxacin is another fluoroquinolone antibacterial developed exclusively for animals (146). It is administered either by parenteral route to cattle, swine, sheep and rabbits, or by the oral route to cattle, swine, rabbits, chickens, and turkeys (147). Although it is not allowed for use in dairy cows, enrofloxacin is also used in some countries for treatment of coliform mastitis in lactating cows. In addition, enrofloxacin has received growing attention during the last years for its potential against several fish pathogens (148). 

In lactating cattle, mean residue levels of thiabendazole and 5-hydroxy-thiabendazole in milk were found to be 5007 and 168 ppb, respectively, 12 h after dosing, decreasing to 20 and 25 ppb at 84 h after dosing. In sheep, 7 days after oral administration of thiabendazole, no residues of the drug were found to be present in muscle, liver, and kidney tissues. 

In sheep given a dose of 15 mg/kg bw, a depletion pattern similar to cattle was observed, but total residues in all tissues were lower at all time points, depleting in liver from around 16 ppm 1 day after dosing to 700 and 170 ppb 4 and 20 days after dosing, respectively. In lactating cattle, total residues in milk were nearly 5 ppm 11 h after administration of a 15 mg/kg bw dose, reducing to 640 and 35 ppb after 35 and 72 h, respectively. 

Other hormones are used for increasing the milk production and efficiency of lactating dairy cows. In the United States an estimated 63% of all cattle and about 90% of feedlot animals are implanted witli growth hormones. Beef and sheep may be also implanted but not swine. When implants are used in young... 

Gil, A. and Sanchez-Mendina, F. 1981. Acid-soluble nucleotides of cow s, goat s and sheep s milks at different stages of lactation. J. Dairy Res. 48, 35-44. 

Vernon, R.G., Faulkner, A., Finley, E., Pollock, H., Taylor, E. 1987. Enzymes of glucose and fatty acid metabolism of liver, kidney, skeletal muscle, adipose tissue and mammary gland of lactating and non-lactating sheep. J. Anim. Sci. 64, 1395-1411. 

In sheep and cattle, a condition known as heart disease occurs when these animals graze on plants containing abnormally high amounts of molybdenum. Dietary levels of 10 ppm molybdenum and higher can cause teart disease. Symptoms that may occur within 24 h include weakness and diarrhea. Longer exposure can lead to decoloration of hair, skeletal deformities, sterility due to damage to testicular interstitial cells, poor conception and deficient lactation. 

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