Milk production and composition, ovarian function, and prostaglandin secretion of dairy cows fed omega-3 fats.

Four multiparous Holstein cows were used in a 4 x 4 Latin square experiment to study the effects of fat sources rich in omega-3 fatty acids on milk production and composition, follicular development, and prostaglandin secretion. All cows were fed a total mixed diet containing 60% grass silage and 40% concentrate. The four treatments were concentrates based either on Megalac, formaldehyde-treated whole linseed, a mixture (50:50, oil basis) of fish oil and formaldehyde-treated whole linseed, or no fat source in the concentrate but with 500 g per day of linseed oil being infused into the duodenum. Feed intakes and milk yield were similar among treatments. In general, the lowest digestibility was observed for the formaldehyde-treated whole linseed treatment. Feeding fish oil decreased milk fat and protein percentages. Alpha-linolenic acid increased from 1.0 to 13.9% of milk fatty acids with linseed oil infusion. This confirms the high potential to incorporate alpha-linolenic acid into milk, and suggests that the formaldehyde treatment had little effect to limit biohydrogenation in the rumen. Increasing the supply of alpha-linolenic acid to these cows did not result in an increase in the concentration of eicosapentaenoic acid in milk. Levels of 13,14-dihydro-15-keto-PGF2alpha in plasma were higher for cows receiving formaldehyde-treated linseed and fish oil. Increases in this metabolite in response to oxytocin challenge, tended to be lower for cows given linseed either as sole oil supplement in the diet or as a duodenal infusion of linseed oil. Follicle dynamics were similar among treatments. Larger corpora lutea (CL) were found with cows that received high levels of omega-3 fatty acids through the diet as formaldehyde-treated linseed or as a mixture of formaldehyde-treated linseed and fish oil, although CL were smaller when cows were infused with linseed oil into the duodenum. These results suggest that the improvement in gestation rate that was observed when feeding increased levels of alpha-linolenic acid in earlier work may partly result from lower levels of production of the dienoic prostaglandin PGF2alpha.

Effect of cultivars on in vitro and ruminal degradation of the nitrogen fraction in birdsfoot trefoil silage.

Experiments were carried out to determine the effects of tannin content on N fractions and DM digestibility of birdsfoot trefoil harvested at 20% bloom stage. Five trefoil cultivars, harvested in both June and August, were used: Upstar, Mirabel, Empire, Leo, and Bt-8861. Forage was ensiled in 1.3-kg laboratory silos for 60 d with 4 silos per cultivar and harvest. Concentrations of DM and tannin in forage were determined prior to ensiling, and N fractions, DM digestibility, and pH in silage were also determined. Tannin concentration and protein N content of silage were lower in Empire than in the other cultivars. Ruminal degradability of DM and CP of Empire (low tannin) and Upstar (high tannin) birdsfoot trefoil were estimated with two fistulated cows using nylon bags that were incubated < or = 96 h. The DM-soluble fraction of Empire was significantly lower than that of Upstar for the first harvest only. This difference was partly due to the high proportions of dry shoots. The CP-soluble fraction of Empire was higher than that of Upstar, but the percentage of CP that was potentially degradable in the rumen was lower for Empire. This difference could result in different CP availability over time even for similar effective degradability of CP. Tannin had no additional effect on total CP degradability in the rumen.

Buserelin alters the development of the corpora lutea in cyclic and early postpartum cows.

Changes in proportions of luteal cells after buserelin treatment were studied in the corpus luteum (CL) that was present at the time of treatment (CLP) and in the buserelin-induced CL (CLI) of cyclic and acyclic postpartum cows. On d 0 of the experimental period, eight cyclic (Cyc-sal) cows were injected with saline, whereas eight cyclic (Cyc-bus) cows and eight acyclic (Acyc-bus) cows were treated i.m. with 8 micrograms of buserelin. On d 3 or 6, ovaries were collected and stained using histological techniques. As determined with the point-counting method, the number of nuclei in the CLP was similar on d 3 in Cyc-bus and Cyc-sal groups but was lower (treatment x day, P < .001) in the Cyc-bus group than in the Cyc-sal group on d 6. The volume of the CLP was similar on d 3 in the two groups but was greater (treatment x day, P < .04) in the Cyc-bus than in the Cyc-sal group on d 6. The number of nuclei in the CLI was greater (P < .001) in cyclic than in acyclic cows on d 3 and 6 after treatment. The volume of the CLI was lower (P < .001) in cyclic than in acyclic cows on d 3 and 6. Buserelin did not change the profile of progesterone in cyclic cows from d 0 to 6, but concentrations of progesterone increased (P < .01) in acyclic cows 3 to 6 d after buserelin treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of corpus luteum and induced ovulation on ovarian follicular dynamics in postpartum cyclic cows treated with buserelin and cloprostenol.

The influence of the corpus luteum (CL) at the time of buserelin treatment and of buserelin-induced ovulation on the dynamics of ovarian follicular development was determined in 18 postpartum cyclic beef cows injected i.m. with 8 micrograms of buserelin on d 0 (d of treatment) and with 500 micrograms of cloprostenol (PGF) 6 d later. From d 0 to onset of estrus, ovaries were examined ultrasonographically, and blood samples were collected daily. Number of medium (5 to 10 mm) follicles and diameters of the two largest (F1 and F2) follicles in each cow were recorded. Cows were grouped according to the presence (CL+) or absence (CL-) of an active CL before buserelin injection and the presence (OV+) or absence (OV-) of a buserelin-induced ovulation (OV). Three groups were formed: CL-OV+ (n = 8), CL+OV+ (n = 6), and CL+OV- (n = 4). Buserelin induced an ovulation in all CL- cows (progesterone [P4] < .3 ng/mL) and in CL+ cows that had P4 < 4 ng/mL but did not in CL+ cows that had P4 > 8 ng/mL. Within CL+ cows, buserelin-induced ovulation (OV+) was associated with a smaller (P < .0001) increase in F1 and F1-F2 diameters and a transient increase in the number of medium follicles that was greater (P < .03) and of a longer duration (P < .01) than in OV- cows. After PGF, the increase in F1 and F1-F2 diameters was still greater in OV+ than in OV- cows (day x OV; P < .05). In all cows, the selection of the preovulatory follicle occurred before PGF injection. Results indicate that a buserelin-induced ovulation was dependent on P4 concentrations at the time of treatment. Subsequently, ovarian follicular dynamics were altered by a GnRH-induced ovulation, but emergence and selection of a large growing follicle occurred in all cows within 6 d of treatment. This follicle became the preovulatory follicle following PGF-induced luteolysis.

Utilization of grass silage by cattle: effect of supplementation with different sources and amounts of protein.

Forty-eight crossbred beef steer calves, initial live weight of 260 kg, were used to examine production responses when grass silage was supplemented with fish meal (FM) or soybean meal (SBM) during a 210-d feeding period. The silage was available on an ad libitum basis either alone or supplemented with 100, 225, 350, or 500 g of FM or 600 g of SBM/d. Increasing levels of FM resulted in a linear increase in live weight gain (P < .001) and gain:feed ratio (P < .001). The FM supplementation had no effect (P = .79) on silage DM intake. The FM supplement increased plasma albumin concentration (P < .05) but did not affect plasma glucose (P > .20) The steers were shipped to market when they had 8 mm of fat over the longissimus muscle as determined by ultrasound. Sensory evaluation of roasts from steers fed 0, 225, 350, or 500 g/d of FM indicated a positive linear (P < .01) increase in flavor and decrease in juiciness as FM level increased. There were no differences (P > .15) in live weight gain, intake, or gain:feed ratio between isonitrogenous supplements of FM and SBM. However, the additional gain resulting from SBM and FM indicated that, on a crude protein basis, SBM was approximately 80% as effective as FM in increasing live weight gain in steers fed grass silage.

Plasma 1,25-dihydroxyvitamin D, insulin-like growth factor-1, calcium, magnesium and phosphorus concentrations in pregnant beef cows and calves from a herd with a known history of congenital joint laxity and dwarfism.

An investigation was undertaken to ascertain the possibility of a relationship between calcium, inorganic phosphorus, magnesium, 1,25-dihydroxyvitamin D [1,25(OH)2D], and insulin-like growth factor-1 (IGF-1) concentrations in blood plasma and occurrence of congenital joint laxity and dwarfism (CJLD) in young cattle. Pregnant cows were fed hay (30 cows) or grass silage (122 cows) during winter months (October 15 to calving in March). Blood samples were taken from cows on seven occasions during the experiment and 48 hours after calving, and from calves at birth, and at seven, 14 and 56 days old. Five per cent of calves born (six of 122) to cows fed grass silage and none born to cows fed hay were affected by CJLD. The diet and health status of calves were not significantly (P greater than 0.05) associated with the plasma concentration of 1,25(OH)2D. The plasma calcium concentration declined with age of the calves (P less than 0.05) but was not affected by the occurrence of CJLD. Plasma phosphorus and magnesium concentrations in calves born to cows fed silage were higher (P less than 0.05) than in those born to cows fed hay. At birth and seven days old, plasma phosphorus concentrations were higher (P less than 0.05) in CJLD-affected calves than in healthy calves but the plasma concentration of IGF-1 was not different (P greater than 0.05). It was concluded that the high plasma phosphorus concentrations in CJLD-affected calves and their dams could be related to the aetiology of the CJLD condition in calves.

Utilization of grass silage by growing cattle: effect of a supplement containing ruminally protected amino acids.

Sixteen crossbred steers (278 +/- 4.9 kg) were used to determine the influence of supplemental ruminally protected lysine and methionine on performance of growing cattle fed grass silage. During the 154-d experiment, all steers were allowed ad libitum consumption of a good-quality grass silage during the first 70 d and of a lesser-quality silage during the remaining 84 d of the trial. The steers received a supplement of .5 kg/d of barley with or without a mixture of ruminally protected amino acid (RPAA) containing 8.2 g of lysine and 2.6 g of methionine. Compared with controls, steers supplemented with RPAA showed 16.3% improved (P less than .03) ADG (.92 vs 1.07 kg/d). Dry matter intake was not affected (P greater than .50) by treatment and averaged 2.03% BW across treatments. Supplementation with RPAA improved feed/gain by 13.6% (7.88 vs 6.81 for control and RPAA treatments, respectively, P less than .01). Plasma levels of methionine, lysine, arginine, and glutamic acid were higher (P less than .05) and of histidine were lower (P less than .001) when RPAA were fed. These results indicate that feeding RPAA can improve the performance of growing steers fed grass silages of varying qualities.

Assessment of the role of manganese in congenital joint laxity and dwarfism in calves.

Pregnant beef cows were winter-fed (November 15 to calving) hay (24 cows), red clover silage (21 cows) or grass silage (52 cows). Blood samples were taken from each cow in December and February. A condition of congenital joint laxity and dwarfism was observed in 38% and 28% of calves born to cows fed red clover silage and grass silage, respectively. None of the calves born to hay-fed cows were affected by the condition. The congenital joint laxity and dwarfism was associated with a lower serum manganese concentration in silage-fed cows than in hay-fed cows. However, manganese concentrations were similar in red clover silage, grass silage and in hay. A lower bioavailability of manganese in silages other than in hay, resulting in an apparent manganese deficiency in silage-fed cows, is suggested as a possible factor contributing to the etiology of congenital joint laxity and dwarfism in calves.

Congenital joint laxity and dwarfism: A feed-associated congenital anomaly of beef calves in Canada.

Five feeding trials were performed on three ranches to determine if a distinctive, recurring, congenital anomaly in beef calves was associated with feeding clover or grass silage without supplementation to pregnant cows overwinter. The anomaly, termed congenital joint laxity and dwarfism, was characterized at birth by generalized joint laxity, disproportionate dwarfism, and occasionally, superior brachygnathia. The anomaly had been documented for several consecutive years on these ranches and affected 2-46% of the calf crop.Pregnant cows were divided randomly into feeding groups, and the number of abnormal calves in each group was tabulated. Supplementation of the overwinter grass/clover silage diet with hay (2.5-4.5 kg/head/day) and rolled barley (0.75-1.5 kg/head/day) eliminated the problem. Supplementation of grain, without hay, was not as effective. Varying the proportions of grass and clover in the silage, and the age of the silage, did not alter the teratogenic potency of silage. Vitamin D(3) supplementation did not reduce the risk of the condition. The definitive cause of congenital joint laxity and dwarfism was not determined.

Plasma vitamin D3 response in cattle and sheep exposed to ultraviolet radiation.

Plasma levels of vitamin D3 were determined in a group of 10 cows housed indoors and exposed during the winter to ultraviolet irradiation (UVR). Exposure to UVR was associated with marked rises in plasma vitamin D3 concentrations. The pattern and magnitude of the plasma vitamin D3 response to UVR exposure in sheep raised in total confinement was also investigated. Exposure to sun lamps produced a significant increase in sheep plasma vitamin D3 concentrations. There was no significant difference in the plasma levels of vitamin D3 due to length of time of exposure to UVR.

Factors affecting the calcium, magnesium and phosphorus content of beef cow milk.

This paper reports the calcium, magnesium and phosphorus content of milk from Shorthorn cattle during the five month calf nursing period as well as the effect of prepartum administration of a single intramuscular dose of vitamin D3 or of 25-hydroxyvitamin D3 on the milk mineral constituents. The colostrum of the group which received 25-hydroxyvitamin D3 was found to contain a higher percentage of calcium on the second and third day than the colostrum of control cows or those receiving D3. No differences occurred in colostrum magnesium or phosphorus contents due to prepartum treatment. Calcium, magnesium and phosphorus concentrations were all high in the first day of lactation, but declined until the third day after parturition. Milk calcium, magnesium and phosphorus content of individual cows was not uniform throughout the lactation and the variation was different for different cows.

Hypomagnesaemia in beef cows wintered in Ontario.

A field experiment was undertaken in northern Ontario in order to assess the magnesium status of beef cattle raised in the area. Magnesium status was assessed using several criteria including blood and urine magnesium levels, and bone biopsy samples. Eighteen groups each containing four pregnant Shorthorn beef cows were used. Each of the following three mineral feeds were offered to six groups throughout the experiment: a mineral feed without magnesium, a mineral feed containing 8% magnesium in the form of magnesium oxide and the third containing sequestered magnesium with a magnesium level of about a tenth of that in the mineral feed containing magnesium oxide. During the winter, when the cows were housed indoors, they were fed grass silage. Six groups, two of each mineral feed, remained indoors throughout the summer. The other 12 groups were turned out to pasture on May 25 and continued receiving the appropriate mineral feed. There were no differences in serum magnesium owing to magnesium-supplementation treatments observed at any time during any experiment. Serum magnesium levels fell drastically in all groups before the cows were released to pasture, implying that the hypomagnesaemic condition was attributable to the stress of yarding. The rate of recovery from hypomagnesaemia was slower in the cows released to pasture than in those kept indoors. Urine samples from cows returned to the pasture were indicative of low magnesium status. At the end of the experiment, the magnesium levels in the bones of the housed animals were higher than for those on pasture. In spite of severe cases of hypomagnesaemia, no clinical signs of this metabolic condition were observed.

A silent hypocupremic condition in beef cows fed grass silage and the efficacy of sequestered copper to prevent its occurrence.

Three groups of 18 Shorthorn cows were fed, as a sole maintenance diet, grass silage known to produce hypocupremia. Two of these groups were comprised of pregnant cows and the third group of non-pregnant cows. In late Fall, the cows were grouped in inside pens and had free access to a mineral feed. In the mineral feed offered to one of the groups of pregnant cows, 0.25% of sodium chloride was replaced by sequestered copper. The non-supplemented group of pregnant cows showed a decrease in blood plasma copper over wintered and in April, more than half of the animals in this group were hypocupremic. The average copper intake (in the form of sequestered copper) from the mineral feed of 8.7 mg/cow/day was sufficient to prevent the onset of hypocupremia in four-fifths of the cows in the supplemented group. The non-supplemented, non-pregnant group maintained normal blood plasma copper level throughout winter confinement. On release to pasture in early summer, cows in all groups of cows showed upwards trends in blood plasma copper level. At the end of the pasture season the blood plasma copper levels in all groups of cows were normal. Hematological and morphological studies showed that hematopoiesis of the hypocupremic cows were not affected and that they were not suffering from microcytic hypochromic anemia. It was suggested that the soluble proteins in the grass silage reduced the amount of copper available in vivo. This, together with the heavy physiological demand of copper imposed upon the cows by pregnancy, resulted in hypocupremia.

25-hydroxyvitamin D in plasma of cattle.

Blood samples from 12 Shorthorn heifers, fed a grass silage ration and housed indoors or outdoors, were assayed for 25-hydroxyvitamin D during 9 mo. There was more in plasma during the summer from the outdoor group, reflecting a greater exposure to ultraviolet light and dermal synthesis of vitamin D, the precursor of 25-hydroxyvitamin D. In another experiment, assays were in four groups of six heifers each; 1) control, 2) single oral dose of 1,000,000 IU vitamin D3, 3) injected intramuscularly with 1,000,000 IU of vitamin D3, and 4) free access to a mineral mixture containing 32,000 IU vitamin D3/kg. In all groups, 25-hydroxyvitamin D was higher in plasma in summer than in winter. All heifers given vitamin D had more 25-hydroxyvitamin D in plasma during winter than controls. Animals injected with vitamin D had more 25-hydroxyvitamin D in plasma during part of the winter than those on the other treatments with vitamin D.