Influence of gonadotrophin-induced first oestrus on gilt fertility.

The aim of this study was to determine the association between the oestrous response of pre-pubertal gilts to gonadotrophin injection or boar exposure and their subsequent farrowing rate and litter size. At 154 days of age, randomly selected pre-pubertal gilts received an intramuscular injection of 400 IU equine chorionic gonadotrophin plus 200 IU human chorionic gonadotrophin (PG600(®) ; Merck Animal Health; n = 181). From the remaining pool of animals not treated with hormones, the first gilts showing signs of oestrus were selected to act as controls (n = 201). Boar exposure began at 155 days of age for both groups, and gilts were bred at a weight of approximately 130 kg. Comparisons were made between PG600(®) -treated gilts exhibiting oestrus or not within 7 days post-injection (early and late responders, respectively) and control gilts exhibiting oestrus or not within 30 days after beginning of boar exposure (select and non-select control gilts, respectively). By 162 days, oestrus was detected in 67.5% of PG600(®) -treated gilts compared with 5.7% of control gilts (p < 0.0001). The proportion of animals observed in oestrus at least three times before breeding was greater for select control gilts compared with early and late responder PG600(®) -treated gilts (p ≤ 0.001). There were no significant differences in farrowing rate and litter size between the four treatment groups. These data indicate that PG600(®) is an effective tool to induce an earlier oestrus in gilts, that subsequent farrowing rate and born alive litter size compare favourably to that of select gilts and that gilts failing to respond promptly to hormonal stimulation do not exhibit compromised fertility.

Influence of lactation length and gonadotrophins administered at weaning on fertility of primiparous sows.

The aim of this study was to determine the effect of lactation length and treatment with gonadotrophins at weaning on reproductive performance of primiparous sows. After 3 wk of lactation, primiparous sows were either weaned (W3; n=273) or received a 7-d-old foster litter for a further 14 d of suckling (W5; n=199). At final weaning (3 wk or 5 wk lactation) sows were randomly assigned to receive an injection of 400 IU equine chorionic gonadotrophin plus 200 IU human chorionic gonadotrophin (PG600(®); W3 + P; n=108 and W5 + P; n=96) or no injection (W3; n=165 and W5; n=103). Sows were inseminated at first observed estrus after final weaning and 24h later. The proportion of sows showing estrus by 6 d post-weaning was greater (P<0.01) for W3+P (86%) compared to W3 (64%), however, there was not a difference (P=0.13) for W5 + P (79.4%) compared to W5 (69.1%). There was no effect of either lactation length or gonadotrophin treatment on farrowing rates or on the proportion of sows culled before breeding. Total born litter size was smaller (P=0.05) for W3 + P (11.7 ± 0.4) compared to W3 (12.6 ± 0.3). However, sows that lactated for 35 d had larger litters than sows that lactated for 21 d regardless of gonadotrophin treatment (14 ± 0.5 and 14.5 ± 0.4 for W5+P and W5, respectively; P<0.001). These data indicate that for primiparous sows, a longer lactation improves total born litter size at their next farrowing. Gonadotrophin treatment is useful in shortening the weaning to estrus interval but subsequent total born litter size may be negatively affected.

Pre-harvest interventions to reduce the shedding of E. coli O157 in the faeces of weaned domestic ruminants: a systematic review.

Our objective was to use formal systematic review methods to evaluate the efficacy of interventions to reduce faecal shedding of Escherichia coli O157 in post-weaned ruminants by increasing animal resistance. The methodology consisted of an extensive search to identify all potentially relevant research, screening of titles and abstracts for relevance to the research question, quality assessment of relevant research, extraction of data from research of sufficient quality, and qualitative summarization of results. The interventions evaluated included probiotics, vaccination, antimicrobials, sodium chlorate, bacteriophages and other feed additives. There was evidence of efficacy for the probiotic combination Lactobacillus acidophilus NP51 (NPC 747) and Propionibacterium freudenreichii and for sodium chlorate in feed or water. The effectiveness of vaccination varied among studies and among vaccine protocols and there was no consistent evidence to suggest that antibiotic use was associated with a decrease in faecal shedding of E. coli O157, or that current industry uses of antimicrobials were associated with increased faecal shedding. There were an insufficient number of studies available to address the effectiveness of bacteriophages and several other feed additives. In general, few of the primary studies evaluated the interventions under commercial housing conditions with a natural disease challenge, there were inconsistencies in the results among study designs and in some cases among studies within study designs, and a relatively large proportion of publications were excluded based on quality assessment criteria. Few studies reported on associations between the proposed intervention and production parameters, such as average daily gain and feed: gain ratio. While the results suggest that some interventions may be efficacious, there are knowledge gaps in our understanding of the efficacy of pre-harvest interventions to increase animal resistance to E. coli O157 that require further targeted research.