Intact Lambs Research Articles

Renin and angiotensin-like levels in foetal, new-born and adult sheep.

1. Plasma renin (measured as rate of formation of angiotensin I ng/ml.hr(-1) in the presence of added substrate at pH 7.5 and 37 degrees C) was much lower in recently nephrectomized foetal, new-born and older lambs than in intact siblings or other similar lambs.2. Angiotensin II-like concentrations were measured using a superfusion technique in an extracorporeal circuit. Resting concentrations in acute experiments under anaesthesia were deduced by comparison of carotid blood of intact lambs with that from recently nephrectomized lambs.3. Angiotensin II-like activity (mean +/- S.E. of mean, 315 +/- 117 pg/ml.) was readily detectable in foetal blood at 123-138 days gestation. The highest concentrations (mean +/- S.E. of mean 839 +/- 96 pg/ml.) were found in lambs less than 8 hr old, delivered vaginally. The lowest concentrations of angiotensin II-like activity occurred in lambs delivered by Caesarean section (mean +/- S.E. of mean < 123 +/- 12 pg/ml.). Concentrations declined with post-natal age.4. Hypovolaemia as a result of haemorrhage evoked an increase in angiotensin II-like concentrations in foetus, new-born lambs and adult sheep. The greatest increase of angiotensin-like concentrations was seen in new-born lambs. This rise was associated with increase of plasma renin.5. The rise of arterial pressure during bilateral carotid occlusion in new-born lambs was accompanied by an increase of angiotensin II-like concentration.6. It is concluded that the renin-angiotensin system is functional and can be stimulated during intra-uterine life. The increase of angiotensin II-like concentration following parturition is probably transient and associated with the trauma of delivery. This contrasts with observations made in the rabbit which suggest that full functional maturity of the renin angiotensin system is delayed until the second week of life.

Effect of Magnesium and Sulfur upon Cellulose Digestion of Purified Rations by Cattle and Sheep

Fistulated steers and intact lambs were used in an experiment designed to study the effect of magnesium and sulfur upon cellulose digestion and of magnesium upon voluntary feed intake. Purified diets with and without magnesium and sulfur were fed to steers, and rations with and without magnesium were fed to lambs. In vivo cellulose digestion was determined with steers and in vitro digestion measured using inoculum from steers and lambs. Digestion of cellulose was significantly decreased in steers fed the purified rations without added magnesium and sulfur. In vitro digestion was also significantly reduced when rumen fluid from the steers and lambs fed the deficient rations was used as the inoculum for in vitro fermentation. Rumen fluid from lambs fed the complete ration was used for inoculation of a series of in vitro media without magnesium. The serial dilution of magnesium from the original inoculum resulted in a progressive decrease in cellulose digestion. Voluntary intakes of the magnesium-deficient ration were significantly reduced by the third day of consumption. Oral administration of magnesium oxide by capsule to lambs resulted in restoration of appetite, but intravenous injection of magnesium sulfate had a lesser effect.

Suction Strainer Technique in Obtaining Rumen Fluid Samples from Intact Lambs

Suction Strainer Technique in Obtaining Rumen Fluid Samples from Intact Lambs

Volatile Fatty Acid Measurements on the Rumen Contents of Lambs Fed Rations of Various Physical Form

A series of four experiments were conducted with lambs to determine the effects of the physical form of the ration and trace mineral supplementation on in vivo rumen molar proportions of volatile fatty acids. Total volatile fatty acid and pH measurements were also made. The ration contained 67% concentrate and 33% roughage. In two of these studies, fistulated lambs were used and in two studies intact lambs were used. The intact lambs appeared to be the better experimental subjects since, for reasons largely unexplained at this time, the effects of the ration treatments were not as pronounced when fistulated lambs were used. Despite these differences, the trends in all studies were similar. The feeding of pelleted rations produced a narrowed acetate to propionate ratio in comparison to similar ground mixed ration. Long hay rations unexpectedly produced narrower acetate to propionate ratios than ground mixed rations. The percent of butyric acid was reduced and that of propionate raised by the addition of cobalt. Percents of iso-butyrate and iso-valerate were lowered and the percent of valerate raised under conditions that narrowed the acetate to propionate ratios. The total quantity of volatile fatty acids tended to be increased by feeding pelleted rations in comparison to ground mixed rations; however, this was not a consistent effect. Acetate to propionate ratios widened with increased length of time after feeding. Acetate production tended to peak approximately four hours after feeding for most rations. However, total acid production had not peaked by six hours on a long hay ration while a peak for ground mixed or pelleted rations was reached previous to two hours after feeding. Rations containing corn cobs produced narrower acetate to propionate ratios than similar rations containing alfalfa hay.

Observations on mammary development in calves and lambs

The normal course of mammary development has been briefly described, in sheep from 2 months of foetal age to 4 months after birth; and in dairy cattle from the 3-month foetus to calves 6 months old. Observations were also made on a series of udders from ewes during their first pregnancy. A small group of beef calves and a number of freemartins of various ages were also examined.Development was found to be closely similar in the two species, and in both, sex differences were marked.Experimentally it was found that in males of either species castration at birth had little effect on mammary growth, while prolonged treatment with oestrogen gave rise to enlarged teats, dilated cisterns and ducts, and to a certain amount of secretion. Little gland tissue was formed in oestrogen-treated males, and there was no increase in the spreading of mammary tissue from the neighbourhood of the teat.Females of the two species showed a striking difference in their response to experimental treatment. In sheep, removal of the ovaries at birth had no apparent effect on mammary development up to 4 months, while treatment with oestrogen stimulated gland formation in both spayed and intact lambs and also restricted the normal spread of mammary tissue into the udder. In cattle, on the other hand, heifers spayed at birth showed almost complete cessation of mammary development, while implants of oestrogen, in addition to inducing gland formation, promoted the spreading of tissue into the udder pad of the spayed animal.Udder development of freemartins appeared to be similar to that of normal heifers from 5 months foetal age to about a month after birth, but thereafter was more like that of a spayed animal. Removal of the abnormal gonads shortly after birth had no effect, while oestrogen treatment induced development of teats, ducts and glands exactly as in a normal heifer.Comparing small numbers of calves of the two types, it was found that heifers of the beef breed in general showed slightly poorer mammary development than dairy heifers that had been treated in the same way, with more connective tissue and numerous leucocytes in the mammary zone.