Arroyo L J, Gallegos-Sánchez J, Villa-Godoy A, Berruecos J M, Perera G, Valencia J
Facultad de Medicina Veterinaria y Zootecnia, Universidad Nacional Autónoma de México, México 04510, DF, México.
Anim Reprod Sci. 2007 Nov;102(1-2):24-30. doi: 10.1016/j.anireprosci.2006.09.025. Epub 2006 Oct 20.
Under photoperiod regulated conditions, some Pelibuey ewes appear to express estrous cycles continuously throughout the year. Ovulatory activity of Suffolk ewes has not being determined at 19 degrees N. The aim of the present study was to describe the annual reproductive cycle of Pelibuey and Suffolk ewes under natural conditions at 19 degrees N. Ten adult ewes of each breed were maintained under natural environmental conditions, on a constant plane of nutrition and isolated from rams. The ovulatory activity of both breeds was monitored over 2 years (2003 and 2004) by quantifying progesterone concentrations in blood samples taken twice a week. For both breeds, the proportion of ovulating ewes per month and year was analyzed by chi(2). The duration of anestrus was compared between breeds and years by analysis of variance. Correlation of ambient temperature and weight changes with the ovulatory activity was evaluated by regression procedure. Ovulatory activity was different (P<0.05) between breeds from February to July. Pelibuey sheep (60%, 6 of 10) ovulated continuously during the entire study; one animal was eliminated in the second year, due to ovarian follicular cysts and three ewes had anestrous periods from 65+/-46 to 70+/-36 days. Suffolk ewes displayed reproductive seasonality similar to that observed in sheep of the same breed in latitudes greater than 35 degrees . Within breed, reproductive behavior of sheep was similar between years, with the only difference (P<0.05) observed in February for Pelibuey and in July for Suffolk relative to other months. Ambient temperature was not correlated with ovulatory activity. The body weight of Pelibuey ewes was constant during the entire study and was not correlated with ovulatory activity. There was, however, an increase on the body weight of Suffolk ewes, but this variation was not related to ovulatory activity. These findings lead to the conclusion that at 19 degrees N, a high proportion of Pelibuey ewes is capable of ovulating throughout the year, whereas Suffolk ewes undergo seasonal anestrous periods similar to those observed in individuals of the same breed at latitudes greater than 35 degrees . Identification of continuous ovulatory Pelibuey ewes may be the first step for developing a selection program against seasonality to increase lambing frequency.
在光周期调控条件下，一些佩利布韦母羊似乎全年都持续表现出发情周期。在北纬19度地区，萨福克母羊的排卵活动尚未确定。本研究的目的是描述北纬19度自然条件下佩利布韦和萨福克母羊的年度繁殖周期。每个品种的10只成年母羊饲养在自然环境条件下，给予恒定的营养水平，并与公羊隔离。通过对每周采集两次的血样中的孕酮浓度进行定量分析，对两个品种的排卵活动进行了为期2年（2003年和2004年）的监测。对于两个品种，每月和每年排卵母羊的比例采用卡方检验进行分析。通过方差分析比较品种和年份间的乏情期持续时间。通过回归分析评估环境温度和体重变化与排卵活动的相关性。2月至7月期间，两个品种的排卵活动存在差异（P<0.05）。在整个研究期间，佩利布韦母羊（60%，10只中有6只）持续排卵；第二年有1只母羊因卵巢滤泡囊肿被淘汰，3只母羊的乏情期为65±46至70±36天。萨福克母羊表现出与北纬35度以上地区同一品种母羊相似的繁殖季节性。在品种内，母羊的繁殖行为在不同年份相似，仅在2月的佩利布韦母羊和7月的萨福克母羊中观察到相对于其他月份的唯一差异（P<0.05）。环境温度与排卵活动无关。在整个研究期间，佩利布韦母羊的体重保持恒定，且与排卵活动无关。然而，萨福克母羊的体重有所增加，但这种变化与排卵活动无关。这些发现得出结论，在北纬19度地区，很大比例的佩利布韦母羊能够全年排卵，而萨福克母羊经历类似于北纬35度以上地区同一品种母羊的季节性乏情期。识别持续排卵的佩利布韦母羊可能是制定一项针对季节性的选择计划以提高产羔频率的第一步。
