Browsing by Author "Tuñon, Gonzalo Enrique"
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- ItemEffect of premating supplementation with monopropylene glycol on reproductive performance of dairy cows : a field trial : a thesis presented in partial fulfillment of the requirements for the degree of Master of Science in Animal Science at Massey University, Turitea, Palmerston North, New Zealand(Massey University, 2005) Tuñon, Gonzalo EnriqueLow body condition score (BCS) at calving is associated with extended time to resume cycling in dairy cows. Prolonged postpartum anoestrous intervals (PPAI) are the major source of infertility in New Zealand dairy cows. Postpartum supplementation with monopropylene glycol (MPG), under controlled experimental conditions, was previously shown to reduce PPAI in heifers. This experiment tested this treatment in four large commercial dairy herds. During the 6-week period preceding the planned start of mating (PSM; Week 0), cows were drenched either once (MPGxl) or twice (MPGx2) daily with 200 ml MPG, or served as untreated controls (Con). A total of 2,122 cows were included in the analysis. Analyses were confined to the group of cows that were anoestrus at Week 6 or calved between Week - 6 and Week -4 relative to PSM (n = 684 to 714 per treatment). None of the four variables: oestrous behaviour during the treatment period, anoestrous rate one week before PSM, 3-week submission rate or 3-week pregnancy rate were affected by MPG. However, MPG did increase the 6-week and final pregnancy rates (P<0.005). with MPGxl having higher values (74.6% and 92.1%) than MPGx2 (69.1 and 88.5%) and Controls (67.7% and 88.1%), respectively. MPG-treated cows also produced more milk protein than the control-cows, by 0.01 and 0.017 kg of milk protein per day for MPGxl and MPGx2, respectively (P = 0.02), evidence of a metabolic effect of MPG. Recent studies suggest that diets that are optimal for follicle growth are not necessarily optimal for oocyte quality and subsequent embryo survival. It is hypothesised that MPGxl had positive effects on the follicle/oocyte through gonadotrophin-independent mechanisms and that MPGx2 had negative effects on the embryo. Probably the gonadotrophin-dependent effects necessary for ovulation could not be exerted in the present study because MPG was not administered for sufficient time to effect the LH surge. Both change in body condition score between Week - 6 and Week - 1, and proportion of cows that were anoestrus at Week -1, were influenced by herd, age and time of calving (P<0.05) but not by treatment (P>0.1). Treatment did not influence the proportion of anoestrous cows, treated with progesterone, which were inseminated after oestrus detection (n = 263). Change in BCS affected both milk yield and pregnancy rates, with cows that gained BCS producing less milk (P = 0.01) but showing higher 6-week pregnancy rates (P<0.05). This study highlighted that key factors influencing the percentage of anoestrus at PSM are cow age, time of calving and management of the herd.
- ItemImproving the use of perennial ryegrass swards for dairying in Ireland : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Agricultural Science at Massey University, Palmerston North, New Zealand(Massey University, 2013) Tuñon, Gonzalo EnriqueThe main objectives of this thesis were to investigate the effects of grazing severity, treading damage, re-growth interval and pre-grazing herbage mass (HM) on sward and animal performance in four experiments during 2009 and 2010 in Ireland. Experiment 1 investigated three post-grazing sward heights ranging from 3.6 to 4.9 cm during the main grazing season. Herbage accumulated and harvested (11.3 and 11.2 t dry matter (DM)/hectare (ha), respectively) were not significantly affected by grazing severity but there were sward morphological and structural differences. Experiment 2 quantified the effects of treading damage during two seasons, ranging from light to severe damage (3.3 to 13.3-cm hoof-print depths, respectively). Treading damage in a perennial ryegrass (PRG) sward on a well-drained soil did not reduce annual grass DM production. Treading in a creeping bent-dominated sward on a poorly-drained soil resulted in 14 to 51% reductions in cumulative yields depending on frequency and season. Experiment 3 examined the effects of 2-, 3- or 4-week re-growth intervals on herbage production, characteristics and tissue turnover of a PRG sward using marked tillers (n = 240) under a cutting regime. Cumulative HMs were 6.7, 9.1 and 10.4 t DM/ha for the 2-, 3- and 4-week re-growth treatments, respectively. The number of leaves appearing per tiller during the re-growth period was only optimum for the 4-week treatment. Experiment 4 also used marked tillers (n = 360) in a grazing dairy cow experiment during the main grazing season under three target pre-grazing HMs (945, 1,623 and 2,360 kg DM/ha >4 cm). The number of leaves appearing per tiller during the re-growth period was 1.0, 1.9 and 2.4 for low (L), medium (M) or high (H) pre-grazing HM treatments, respectively. Cows grazing L, M or H pre-grazing HM produced 343, 342 and 330 kg milksolids, respectively. Low pre-grazing-HM cows grazed for 90 min/day more than M and H pre-grazing-HM cows but there was no difference in individual intake (16.0 and 15.8 kg DM/cow/day in June and August, respectively). Post-grazing sward height, treading damage, re-growth interval and pregrazing HM can have a significant impact on the sward and on animal performance. The imposition of best management practice leads to a more effective conversion of grass into milk.