Prostaglandin f(2alpha) concentrations, fatty acid profiles, and fertility in lipid-infused postpartum beef heifers

Effect of underfeeding post-partum Charolais beef cows on composition of plasma non-esterified fatty acids

This work was designed to investigate whether the profile of non-esterified fatty acids (NEFA) remains constant in response to underfeeding in beef cows, since in other species mobilization of fatty acids (FA) has been shown to be dependent on fatty acid structure. Twenty-one Charolais cows (multiparous, no. = 16 and primiparous, no. = 5) were assigned to one of two diets (control diet (CD; no. = 11) or restricted diet (RD; no. = 10) which, respectively supplied all or 0·7 of energy and protein requirements) after calving. Blood and composite milk samples were collected weekly before the morning meal over a period of 9 weeks. The cows given RD lost significantly more body weight (P < 0·001) and condition score (P < 0·05) than the cows given CD. Plasma NEFA and urea concentrations were also higher in RD than CD during the experiment (P < 0·05 and P < 0·001, respectively). The level of feeding did not affect plasma insulin and glucose concentrations. Milk FA were affected by feeding level. The proportions of short- and medium-chain FA were lower in RD compared with CD (C8: 0, C10: 0, C12: 0 and C14: 0, P < 0·05 and C14: 1 and C16: 0, P < 0·10) while some of the long-chain FA were higher (C17: 0 and C18: 1, P < 0·001 and C17: 1, P < 0·10). Feeding level affected the profile of FA in plasma NEFA. The proportions of C16: 0 and C18: 1 were higher (P < 0·05) in RD cows compared with CD cows while the proportions of C12: 0, C14: 1, C17: 0, C18: 0 and C18: 2 were lower (P < 0·05). There was a feeding level × time interaction in the proportions of different FA in the plasma NEFA and in the total plasma NEFA concentrations. The differences caused by feeding level gradually disappeared with time. The proportion of C18: 1 in plasma NEFA and the total plasma NEFA concentrations were quadratically positively correlated, while the correlation between C18: 2 and total plasma NEFA was negative. In conclusion, when post-partum beef cattle are underfed, plasma NEFA concentrations increase (indicating lipomobilization) and this increase is associated with an increase in the proportion of oleic acid (C18: 1) in plasma NEFA.

Effects of short-term oilseed supplementation on plasma fatty acid composition, progesterone and prostaglandin F metabolite in lactating beef cows

Twenty-four 3-year-old Angus cows (512.2±21.6 kg) and six ruminally cannulated beef heifers (523.1±16.9 kg) were used to determine the impact of feeding oilseeds starting at the beginning of estrous synchronization until maternal recognition of pregnancy on plasma fatty acid composition. Starting ~60 days postpartum cows were synchronized with the Select Synch+controlled internal drug-release (CIDR) device and timed artificial insemination (AI) protocol. The day CIDR was inserted; cattle were randomly assigned to one of the three treatments being grazing only (CON) or a supplement containing whole soybeans (SOY); or whole flaxseed (FLX). Cattle continued to receive these diets for 28 days. Blood was collected every 3 days until 10 days after insemination and then every day until 18 days after insemination. All cattle grazed a common pasture and supplemented cattle were individually fed their respective supplements once daily. Ruminally cannulated heifers were used to evaluate the impact supplements had on forage intake, which was reduced (P=0.05) with oilseed supplementation. Feeding oilseeds increased total fatty acid intake (P<0.001) across treatments with SOY having greater (P<0.001) 18:2n-6 intake than either CON or FLX. Likewise, cattle fed FLX had greater (P<0.001) 18:3n-3 intake than either CON or SOY. There was a treatment×time interaction (P≤0.05) for all fatty acids identified except for 20:5n-3 (P=0.99). Within 3 days after the start of supplementation, plasma concentrations of 18:2n-6 increased (P<0.001) for cattle fed SOY compared with CON or FLX, whereas flax-fed cattle did not exhibit an increase (P=0.02) until day 15 of supplementation over that of CON. Plasma concentrations for 18:3n-3 was greater (P<0.013) for FLX than both CON and SOY by day 12. Feeding flaxseed tended to (P=0.07) increase and increased (P=0.01) plasma concentrations of 20:4n-6 by day 18 over CON and SOY, respectively. Overall, treatment did not affect serum concentration of progesterone (P=0.18) or prostaglandin F metabolite (P=0.89). However, day after breeding had an effect on serum progesterone (P=0.01) with day 16 after timed AI being lower compared with other days. Feeding oilseeds during the time of estrous synchronization will not only increase the energy density of the diet but will provide key fatty acids around the time of maternal recognition of pregnancy.

Increased prostaglandin response to oxytocin in ewes fed a diet high in omega-6 polyunsaturated fatty acids

Diets high in omega-6 polyunsaturated fatty acids (n-6) are associated with increased prostaglandin F(2α) (PGF(2α)) synthesis in cattle, however, the specific effects on the potential prostaglandin response to an oxytocin challenge in sheep have not been reported. The aim of the current study was to determine whether oxytocin-stimulated PGF(2α) was significantly increased when ewes were fed a diet high in n-6 compared with a control diet low in n-6. Merino x Border Leicester ewes (n = 30) received one of two dietary treatments, either high in n-6 (70 % oat grain) or low in n-6 (control diet, 100 % cereal/legume silage). Ewes consumed the diets for 44 days prior to two consecutive oxytocin challenges. Plasma n-6 and PGF(2α) metabolite (PGFM) concentrations following oxytocin challenge were greater (P < 0.05) when ewes were fed a diet high in n-6 compared with the control diet. A higher availability of n-6 may have lead to an increased in vivo synthesis of PGF(2α), however, further research is required to determine the exact mechanisms involved.

Effect of dietary enrichment with either n-3 or n-6 fatty acids on systemic metabolite and hormone concentration and ovarian function in heifers

The objective of this experiment was to examine the effects of dietary n-3 or n-6 fatty acid (FA) supplementation on blood FA, metabolite and hormone concentrations, follicle size and dynamics and corpus luteum (CL) size. Reproductively normal heifers (n = 24) were individually fed diets of chopped straw and concentrate containing either (i) no added lipid (CON; n = 8); (ii) 2% added fat as whole raw soya beans (WSB, n-6; n = 8); or (iii) 2% added fat as fish oil (FO, n-3; n = 8). Following oestrous cycle synchronisation, blood samples were collected at appropriate times and intervals for the measurement of hormones, FAs and metabolites. On days 15 and 16 of the cycle, animals were subjected to an intravenous oxytocin challenge and prostaglandin F2α (PGF2α) response, measured as venous concentrations of 13,14-dihydro-15-keto PGF2α (PGFM). Dry matter intake and average daily gain were similar among treatments (P > 0.05). Plasma concentration of linoleic acid was highest on WSB (P < 0.05), while eicosapentaenoic (EPA, n-3; P < 0.0001) and docosahexaenoic acid (DHA, n-3; P < 0.0001) were greatest in the FO group. Plasma concentrations of arachidonic acid were higher on FO (P < 0.05) compared with CON and WSB. Plasma triglyceride concentrations increased, while β-hydroxybutyrate (BHBA) decreased with time on all diets (P < 0.05). There was a diet × time interaction (P < 0.01) for non-esterified fatty acid (NEFA) concentrations. Plasma cholesterol was higher on WSB and FO (P < 0.01) compared with CON. Progesterone (P4) and oestradiol (E2) concentrations, as well as follicle growth rate and CL diameter were similar across diets (P > 0.05). There was a diet × day interaction for PGFM (P < 0.01). When corrected for systemic E2 : P4 ratio, day 15 concentrations of PGFM were higher in the WSB group at 15 and 30 min (P < 0.01) post oxytocin administration compared with CON and FO, which were similar (P > 0.05). Concentrations of PGFM on day 16 were similar for WSB and FO and were greater than CON at 15 (P < 0.01) and 45 min (P < 0.05) post oxytocin administration, and at 30 min for FO (P < 0.05). With the exception of PGFM, dietary lipid source did not affect the reproductive variables measured.

Differential Effects of n-3 and n-6 Fatty Acids on Prostaglandin F2 Production by Bovine Endometrial Cells

Recent studies have implicated n-3 polyunsaturated fatty acids in the reduction of eicosanoid production in the bovine uterus. The objective of this study was to determine whether the effect of eicosapentaenoic acid (EPA; C(20:5), n-3) on PGF2alpha production by bovine endometrial (BEND) cells is influenced by the quantity of linoleic acid (C(18:2), n-6) in the incubation medium. Confluent BEND cells were incubated in the absence (control) or presence of 100 microM of EPA for 24 h. After incubation, cells were rinsed and then stimulated with phorbol 12,13-dibutyrate (PDBu; 100 ng/mL) for 6 h. Additional sets of culture dishes were treated with a combination of EPA and increasing n-6/n-3 fatty acid ratios for 24 h and then challenged with PDBu for 6 h. The PDBu stimulated PGF2alpha secretion and upregulated steady-state concentrations of prostaglandin endoperoxide synthase-2 and peroxisome proliferator-activated receptor delta mRNA within 6 h. Preincubation of BEND cells with EPA for 24 h decreased PGF2alpha response to phorbol ester, but had no detectable effects on prostaglandin endoperoxide synthase-2 or peroxisome proliferator-activated receptor delta mRNA abundance in PDBu-stimulated BEND cells. The inhibitory effect of EPA on PGF2alpha production was reverted in BEND cells treated with an increasing n-6-to-n-3 fatty acid ratio. Findings indicate that the net inhibition of endometrial PGF2alpha bioynthesis by n-3 fatty acids may vary depending on the ratio of n-6 to n-3 fatty acids in the uterus.

Effect of offering rumen-protected fat supplements on fertility and performance in spring-calving Holstein-Friesian cows

The objective of this study was to evaluate the effect of two different rumen-protected fat supplements, on reproductive performance and milk production, in grass-based spring calving cows. Two hundred and one Holstein-Friesian cows with an average lactation number of 3.6 (20% first lactation, 16% second lactation and 64% third lactation or greater) were grouped into blocks of three on the basis of calving date, lactation number and previous lactation milk yield for cows of second lactation or greater and on the basis of calving date for first lactation animals. From within-blocks individual animals were assigned at random, within 10 days post-calving, to one of the following three treatments: (1) Megalac Plus 3% (MP; 0.4kg/day, containing Ca salt of palm fatty acids and Ca salt of methionine hydroxy analogue), (2) Megapro Gold (MPG; 1.5kg/day, containing Ca salt of palm fatty acids, extracted rapeseed meal and whey permeate), and (3) Control (C; unsupplemented). Cows were supplemented for on average 103 days (range 54-134 days). The average milk yield over the first 12 weeks of lactation was higher (P<0.05) for both fat supplements compared to C and was higher for MP compared to C over the full lactation. Both supplements reduced (P<0.05) milk protein concentration over the first 6 weeks of lactation. MPG increased (P<0.05) conception rate to first service compared to C. Conception rate to first service was similar (P=0.14) on MP compared to C. For pregnancy to second service, C had a higher (P<0.05) conception rate than MP. There were no significant differences between treatments in overall pregnancy rate, services per conception, number of cows served in the first 3 weeks of the breeding season or the 6-weeks in-calf rate. Comparing the combined fat treatments to C resulted in a higher (P<0.05) conception rate to first service for the fat treatments but no significant difference in overall pregnancy rate. In conclusion, fat supplements increased conception rate to first service but did not significantly affect the proportion of cows pregnant at the end of the breeding season.

Effects of calcium salts of fatty acids and calcium salt of methionine hydroxy analogue on plasma prostaglandin F2alpha metabolite and milk fatty acid profiles in late lactation Holstein-Friesian cows

Effects of a dietary lipid supplement containing calcium salts of fatty acids and methionine hydroxy analogue on plasma prostaglandin F2alpha (PGF2alpha) metabolite (PGFM) and milk fatty acid profiles were examined in 40 late lactation, nonpregnant, Holstein-Friesian cows for a period of 70 days. Effects on milk production, milk composition, and blood metabolites were also examined. Cows were paired on the basis of lactation number (first lactation, n = 8; second lactation, n = 32) and randomly assigned from within pairs to one of two dietary treatments: unsupplemented control (C) or 400 g per cow per day of the lipid supplement (S). Cows receiving the supplement had higher (P < 0.05) total milk production, total fat production (kg), and total lactose production (kg). Plasma cholesterol was significantly higher (P < 0.01) after 30 days of treatment in cows receiving the supplement. Cows receiving the supplement had lower (P < 0.01) concentrations of short chain milk fatty acids (C4:0 to C14:1) and higher concentrations of long chain fatty acids (C18:1 and C18:2; P < 0.01) than control animals. Oxytocin-induced prostaglandin release on Day 16 postovulation was increased (P < 0.01) in cows receiving the supplement. In conclusion, supplementation with calcium salts of fatty acids and methionine hydroxy analogue significantly increased milk yield and plasma PGFM.