255 EFFECT OF THE TYPE OF DIETARY FATTY ACID (α-LINOLENIC ACID OR LINOLEIC ACID) ON THE NUMBER AND THE QUALITY OF OOCYTES COLLECTED BY OVUM PICKUP AND ON IN VITRO EMBRYO PRODUCTION BY DAIRY HEIFERS

Abstract

A supplement of dietary fat can improve oocyte quality in ruminants. However, to our knowledge, the effect of the type dietary fat (differing in fatty acid profile) on oocyte and embryo production has never been reported in cattle. Therefore, in this study the effect of the type of fat supplement on the number and quality of oocytes collected by ovum pickup (OPU) and on the production of embryos was investigated in Holstein heifers. The experiment was conducted over 2 years: year 1: 8 heifers, and year 2: 10 heifers (16 to 20 months old, body weight 368 ± 8.2 kg and BCS 2.3 ± 0.1). Heifers were given a diet of hay (67% DM) and a concentrate (33% DM). The concentrate (130 g fat/kg DM) was formulated with either extruded linseeds (L, rich in α-linolenic acid (ω-3 fatty acid),n = 9) or extruded soybeans (S, rich in linoleic acid (ω-6 fatty acid), n = 9). Oocytes were collected by OPU for 6 weeks (2 sessions/week) and their morphological quality was assessed (Q1, excellent; Q2, good; Q3, fair; and Q4, low). The oocytes from one session/week were frozen and those from the other session were used to produce embryos (in vitro maturation and fertilization). Embryo quality was judged following IETS criteria (EQ1, excellent; EQ2, good; EQ3, fair; and EQ4, low). Blood samples were collected weekly throughout the experiment for the analysis of insulin, insulin-like growth factor-1, glucose, non-esterified fatty acids, β-hydroxybutyrate, and urea. Statistical analysis was performed on the growth rate, BCS, hormone, metabolite, and fatty acid data and on the oocyte and embryo data using Split plot ANOVA. Growth rate was not affected by diet (S, 0.93 ± 0.21 kg d^-1 vs. L, 0.90 ± 0.21 kg d^-1), and there was no effect of dietary treatment on plasma hormone and metabolite concentrations. However, treatment L increased the proportion of α-linolenic acid (P < 0.0001), and treatment S increased the proportion of linoleic acid (P < 0.0001) in the plasma. Neither the oocyte characteristics (number of oocytes collected, 5.3 ± 1.0 vs. 5.7 ± 1.0; their quality: Q1, 1.1 ± 0.3 vs. 1.0 ± 0.3; Q2, 1.8 ± 0.3 vs. 1.6 ± 0.3; Q3, 1.4 ± 0.4 vs. 2.1 ± 0.4; and Q4, 1.0 ± 0.2 vs. 1.1 ± 0.2; and oocytes inseminated, 4.4 ± 0.8 vs. 5.1 ± 0.8, and cleaved, 3.4 ± 0.7 vs. 3.5 ± 0.7 per heifer per session; L vs. S, respectively) nor the embryo characteristics (number of embryos, 1.1 ± 0.3 vs. 0.9 ± 0.3; their quality: EQ1, 0.4 ± 0.1 vs. 0.3 ± 0.1; EQ2, 0.4 ± 0.1 vs. 0.3 ± 0.1; EQ3, 0.2 ± 0.1 vs. 0.3 ± 0.1; and EQ4, 0.04 ± 0.03 vs. 0.05 ± 0.03 per heifer per session; L vs. S, respectively) were affected by dietary treatment. In conclusion, under our experimental conditions, the type of fatty acid (ω-3 vs. ω-6) does not modify significantly the numbers of oocytes and embryos produced by OPU and their quality in dairy eifers.