Semester

Fall

Date of Graduation

2013

Document Type

Thesis

Degree Type

MS

College

Eberly College of Arts and Sciences

Department

Animal and Nutritional Sciences

Committee Chair

Emmett K. Inskeep

Committee Co-Chair

Eugene E. Felton

Committee Member

Marlon Knights

Abstract

A study, conducted in two replicates, examined the effects of an artificial photoperiod on puberty in fall-born ewe lambs. Replicate I was initiated in December 2011 with prepubertal Dorset ewe lambs (n = 44). Replicate II was initiated beginning in December 2012 and included prepubertal Dorset, Suffolk x Dorset and Texel x Dorset ewe lambs (n = 52). All lambs were weighed at the initiation of each replicate and randomized to one of two treatments, control or treated, based on age, weight, breed and type of birth and rearing. Control ewe lambs were housed in a barn with exposure to natural photoperiod from December 16, 2011 until March 24, 2012 in replicate I and from December 17, 2012 until March 17, 2013 in replicate II. Treated ewe lambs were housed in a section of the same barn, but exposed to natural and supplemental light (~100 lux at lamb eye level) to produce an artificial photoperiod of 16 hours light and 8 hours dark for 14 weeks, from December 16, 2011 until March 24, 2012 in replicate I and from December 17, 2012 until March 25, 2013 in replicate II. Following completion of light treatment, each treated female received a silastic implant containing 20 mg of melatonin (Melovine), subcutaneously in the ear. Light intensity during the artificial lighting period for the treated group was measured, at random intervals, throughout the experiment and had an average value of ~100 lux, at ewe lamb eye level as measured by a Digital Light Meter (LX1010B). Growth of the lambs was monitored, as both weight and age are integral components of puberty. All ewe lambs were weighed at four time points during the study, including onset for each replicate, weaning, light termination and CIDR insertion. Ewe lambs were synchronized for estrus with the use of CIDR-G inserts, administered on May 18 of each year. On May 23 of each year CIDR implants were removed and intact fertile rams introduced. Rams were removed on June 19, 2012 or June 25, 2013 after allowing a breeding period of two opportunities for behavioral estrus. Pregnancy was determined by transrectal ultrasonography 25 days after removal of the rams. Progesterone was assayed, on all animals at four time points, using a radioimmunoassay. Plasma melatonin was assayed, in a subset of both treated and control females in replicate I prior to light termination, using an ELISA method. At light termination; treated females, in replicate I, weighed an average of 52.9 +/- 1.6 kg compared to 48.1 +/- 1.6 kg for control females (P < 0.05). Extended light photoperiod increased weight gain in Replicate I, but not in Replicate II. Overall, fall-born Dorset ewe lambs (56 to 57%) conceived their first spring with no effect of the artificial photoperiod/melatonin treatment. Suffolk- and Texel-sired lambs from Dorset ewes did not have the out-of-season breeding ability seen in the purebred Dorset ewe lambs, even with the artificial photoperiod/melatonin treatment; only 2 0f 14 (14%) of Suffolk-sired ewe lambs conceived.

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