Cattle are fed moderate amounts of long chain fatty acids (FA) with the objective to enhance lactation and growth; however, recent interest on lipid feeding to cows has focused on reproduction, immunity and health. Increasing the caloric density of the ration by fat feeding has generally improved measures of cow reproduction, but when milk yield and body weight losses were increased by fat supplementation, positive effects on reproduction were not always observed. Feeding fat has influenced reproduction by altering the size of the dominant follicle, hastening the interval to first postpartum ovulation in beef cows, increasing progesterone concentrations during the luteal phase of the oestrous cycle, modulating uterine prostaglandin (PG) synthesis, and improving oocyte and embryo quality and developmental competence. Some of these effects were altered by the type of FA fed. The polyunsaturated FA of the n-6 and n-3 families seem to have the most remarkable effects on reproductive responses of cattle, but it is not completely clear whether these effects are mediated only by them or by other potential intermediates produced during rumen biohydrogenation. Generally, feeding fat sources rich in n-6 FA during late gestation and early lactation enhanced follicle growth, uterine PG secretion, embryo quality and pregnancy in cows. Similarly, feeding n-3 FA during lactation suppressed uterine PG release, and improved embryo quality and maintenance of pregnancy. Future research ought to focus on methods to improve the delivery of specific FA and adequately powered studies should be designed to critically evaluate their effects on establishment and maintenance of pregnancy in cattle.

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Dietary sources of fatty acids were evaluated for their influence on oocyte quality and follicular development using 54 lactating cows in summer. Fat supplements were 1) sunflower oil (80% cis 18:1), 2) Ca salt of transoctadecenoic acids (57% trans 18:1), 3) Ca salt of vegetable oils (30% 18:2), and 4) linseed oil (56% 18:3 and 16% 18:2). Fats were fed at 1.35% of dietary dry matter beginning at 5 wk prior to expected calving date and at 1.5% (oils) and 1.75% (Ca salts) of dietary dry matter for 15 wk after parturition. Four days following a programmed induced ovulation, 5 transvaginal oocyte aspirations were performed 3 or 4 d apart. Three days after the last aspiration, PGF2alpha was injected, followed 3 d later by a GnRH injection and a timed artificial insemination (d 0) 16 to 20 h later. For the first 4 aspirations, oocytes grading 1 or 2 were used for in vitro embryo production. Total cell number and the proportion of terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL)-positive blastomeres were analyzed at d 8. At the fifth aspiration, the occurrence of metaphase II, group II caspase activity, and TUNEL labeling were determined after oocyte maturation. A total of 1,011 oocytes were collected. The proportion of oocytes with high caspase activity was greater for grade 3 compared with grades 1 and 2 (37.5 vs. 1.54 and 1.61%). Feeding polyunsaturated fatty acids, as compared with monosaturated fatty acids, failed to affect oocyte quality, as demonstrated by subsequent embryo development. Cows fed 18:2- or 18:3-enriched diets had a larger preovulatory follicle at insemination and subsequent volume of the corpus luteum compared with those fed cis 18:1 or trans 18:1 diets (16.8, 16.2 vs. 15.0, 14.9 +/- 0.7 mm; 7,323, 8,208 vs. 6,033, 5,495 +/- 644 mm3, respectively). The previously documented benefits of polyunsaturated fatty acids on reproductive performance appear to reflect actions at alternative biological windows in lactating dairy cows.

The objectives were to evaluate the effects of differential timing of supplementation of different Ca salts (CS) of fatty acids (FA) on FA profiles of cotyledonary-caruncular tissues, metabolic status, uterine health, pregnancy, pregnancy losses after 2 artificial inseminations (AI), and milk yield. Holstein cows (n=1,380) were assigned randomly to be fed either CS of palm oil (PO) or safflower oil (SO) from 30 d prepartum until 30 d postpartum (dpp) and further randomized to receive either CS of PO or fish oil (FO) from 30 to 160 dpp. Supplementation of CS of FA was at 1.5% of dietary dry matter. Tissues (n=23) and blood (n=32) were collected from a subsample of cows. Blood was collected daily from parturition to 10 dpp and three times weekly thereafter until 30 dpp for analyses of PGF2α metabolite, nonesterified FA, β-hydroxybutyric acid, blood urea nitrogen, and glucose. Cows were evaluated once between 8 to 10 dpp for cervical discharge type. At 43 dpp, cows received 2 injections of PGF2α 14 d apart, followed 14 d later by injections of GnRH at 7 d before and 56 h after an injection of PGF2α with AI at 16 h after the second GnRH injection. All cows received intravaginally a controlled internal drug-releasing device, containing 1.38 g of progesterone, at 18 d after the first AI followed 7 d later by removal of the device and injection of GnRH. Nonpregnant cows at 32 d after AI were injected with PGF2α, followed 56 h later with a GnRH injection and second AI 16 h thereafter. Cows diagnosed pregnant after both AI were re-examined at 60 d of pregnancy to determine pregnancy losses. Milk weights were recorded monthly for all cows. Caruncular n-6:n-3 FA ratio was greater in cows fed SO. Plasma concentrations of metabolites and frequency of cervical discharge type did not differ between PO- and SO-fed cows. Plasma PGF2α metabolite was greater in SO-fed cows at 4 and 7 dpp. Pregnancy per AI at 32 and 60 d post first AI was not affected by diets, but pregnancy loss was less in FO-fed cows. At second AI, pregnancy was greater in FO-fed cows at 32 d and in SO-FO-fed cows at 60 d post AI. Pregnancy loss after second AI was not affected by diets. Overall pregnancy per AI was greater in cows fed SO followed by FO at 60 d of pregnancy and pregnancy loss was reduced in FO-fed cows. Monthly milk yield was greater (0.7 kg/d) in SO-fed cows. In conclusion, strategic feeding of CS of FA during transition and breeding periods can benefit fertility and milk production of lactating dairy cows.

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