The effects of dietary urea on embryo development in superovulated donor ewes and on early embryo survival and development in recipient ewes

Abstract

The aim was to examine the effect of dietary urea on yield and quality of embryos in superovulated donor ewes, and on embryo survival in recipient ewes. Ewes (25 donors and 34 recipients) were offered 1·25 kg of grass meal containing 50 g urea per ewe per day on a group basis; the remaining ewes (30 donors and 32 recipients) received 1·25 kg untreated grass meal per day. After 5 days, ewes were synchronized using a progestagen pessary for 14 days and stimulated with pregnant mare serum gonadotropin. Donors were naturally mated; recipients were detected in oestrus using vasectomized rams. On day 4 following the onset of oestrus, embryos were recovered from donors, graded morphologically and cell number counted. Two embryos of acceptable morphological grade (≥ eight cells on day 4) were then surgically transferred to recipient ewes. Recipients were slaughtered between days 34 and 36 post oestrus. The mean number of embryos recovered per ewe [3·68 (s.e. 0·41) v. 3·83 (s.e. 0·45)] was not different between untreated and urea-treated ewes, respectively. However, urea treatment of donor ewes reduced the mean cell number per embryo (10·27 (s.e. 0·27) v. 8·17 (s.e. 0·29) for untreated and urea-treated donor ewes, respectively, P < 0·001). Similarly, the percentage of embryos recovered that had ≥ 10 cells and their mean cell number was reduced following urea treatment of donor ewes (82/113 (73%) v. 39/93 (42%), P < 0·01 and 11·61 (s.e. 0·20) v. 10·41 (s.e. 0·29), P < 0·001) for untreated and urea-treated ewes, respectively. The diet offered to recipient ewes had no effect on the number of ewes confirmed pregnant (24/32 (75%) v. 28/34 (82%)) or on embryo survival following transfer (45/64 (70%) v. 51/68 (75%) for untreated and urea-treated ewes, respectively, P > 0·05). Excess nonprotein nitrogen in the form of dietary urea reduced embryo quality. However, embryo survival in recipient ewes was not affected when good quality embryos were transferred. This suggests that the deleterious effects of excess dietary urea are due to alterations to the oocyte and (or) the oviductal environment rather than changes in the uterine environment.

Effect of nutrition on plasma lipid profile and mRNA levels of ovarian genes involved in steroid hormone synthesis in Hu sheep during luteal phase1

“…Circulating urea has been negatively associated with fertility. (McEvoy et al, 1997;Fahey et al, 2001;Ferreira et al, 2011), except for Westwood et al's (1998) study. The detrimental effects on reproduction may be mediated in part through the direct effect of urea on the nuclear and cytoplasmic development of the follicle-enclosed oocyte (Santos et al, 2009;Ferreira et al, 2011).…”

Reduced Fertility in High‐yielding Dairy Cows: Are the Oocyte and Embryo in Danger? Part II Mechanisms Linking Nutrition and Reduced Oocyte and Embryo Quality in High‐yielding Dairy Cows*

“…Finally, it has been suggested that such uterine environments are also hostile for the viability and motility of spermatozoa (Westwood et al 1998). Interestingly, Fahey et al (2001) found reduced embryo quality in donor ewes fed high‐protein diets, but the diet of the embryo recipients had no effect on survival of transferred embryos. Hence, they suggested that the adverse effects of urea on embryo quality are likely to be due to deleterious alterations in the environment of the follicle and/or oviduct, rather than due to a changed uterine environment (Fahey et al 2001; Papadopoulos et al 2001).…”

“…Interestingly, Fahey et al (2001) found reduced embryo quality in donor ewes fed high‐protein diets, but the diet of the embryo recipients had no effect on survival of transferred embryos. Hence, they suggested that the adverse effects of urea on embryo quality are likely to be due to deleterious alterations in the environment of the follicle and/or oviduct, rather than due to a changed uterine environment (Fahey et al 2001; Papadopoulos et al 2001). This finding was very recently confirmed in a study of lactating dairy cows (Rhoads et al 2006).…”

Effect of protein degradability on milk production of dairy ewes

“…Urinary urea contributes to environmental pollutants, such as atmospheric ammonia and nitrates in ground water (Tamminga, 1992). Excess RDP can also have negative consequences for the ruminant; excess RDP reduces embryo quality in sheep, possibly related to ovarian steroid concentrations affecting embryo development and transport (Berardinelli et al, 2001;Fahey et al, 2001).…”