Document Type

Dissertation - Open Access

Award Date

2012

Degree Name

Doctor of Philosophy (PhD)

Department / School

Animal Science

First Advisor

Amanda Blair

Abstract

Given the potential variation in forage quantity and quality available to gestating cows, it is possible to encounter periods of nutrient restriction, while supplementation decisions could lead to periods of over-nutrition. Maternal nutrition during mid-late gestation has shown to influence adipose development and myogenesis in the fetuses of various species; however, bovine research is limited. The objective of this experiment was to determine whether maternal nutrition during mid-gestation alters genetic expression of fetal adipogenic and myogenic regulatory factors, resulting in differences in adipose development and muscle characteristics of the bovine fetus. Twenty-two bred Angus crossbred heifers (BW = 527.73 ± 8.3 kg) were assigned randomly to one of three dietary treatments providing 146% (HIGH; n=7), 87% (INT; n=7), or 72% (LOW; n=8) of the energy requirements for growing pregnant heifers, from day 85 to 180 of gestation. Body weight and ultrasound measurements for fat thickness (Ff) and longissimus muscle area (LMA) were recorded to determine changes in dam body condition. Fetuses were removed via cesarean section at day 180 of gestation and fetal weight and crown rump length were recorded. Samples from the longissimus muscle (LM) were excised from the left side of each fetus, diced, snap frozen, and stored at - 80°C for evaluation of expression of select genes using real-time PCR. The expression of PREF-1, PPARy, C/EBP alpha and beta were evaluated as they are essential factors in adipocyte differentiation. The expression of MyoD, Myf5, myogenin, and MRF4 were evaluated as they are essential for myoblast determination and proliferation, as well as myostatin, which mediates myoblast number and fusion. Nutrition has also been shown to influence calpastatin expression in bovine fetuses; therefore expression of the calpain protease system was also quantified. The LM and semitendinosus removed from the right side of each fetus was dissected, fixed in paraformaldehyde and embedded in paraffin. Transverse sections, 10 μm thick, were cut and stained with hematoxylin and eosin to determine fiber area and diameter. The right hind limb of each fetus was removed, frozen and subsequently dissected for composition analysis of the semitendinosus. At trial initiation, dam BW was similar among treatment groups. Final BW was lowest for the LOW dams (P < 0.05); however, final BW for INT and HIGH were similar. Ribfat thickness increased in the HIGH treatment group compared with LOW and INT dams (P < 0.05). Thus, dam weight and composition were influenced by diet during the treatment period; however, dietary treatment did not influence fetal weight or crown rump length (P = 0.45, P = 0.16 respectively). Preadipocyte factor-1 expression was up-regulated in fetal LM (P = 0.001) of HIGH fetuses as compared with INT and LOW. Peroxisome proliferator-activated receptor gamma and C/EBP alpha did not differ as a result of dietary treatment. However, LOW and HIGH fetuses showed increased C/EBP beta expression as compared with INT (P = 0.006, P = 0.05 respectively). Expression of MyoD, Myf5 , and MRF4 were similar between treatments; however, myogenin was more highly expressed (P = 0.04) in the HIGH fetuses as compared with the LOW, which may indicate greater terminal differentiation of myoblasts. No differences were detected between treatment groups for expression of myostatin, m-calpain or calpastatin. However, μ-calpain showed increased expression in fetal LM (P = 0.01) of HIGH fetuses compared with INT, but did not differ from LOW (P = 0.45). Expression of insulin-like growth factor I and II were up-regulated in both the LOW and HIGH fetuses (P = 0.056, P = 0.024 respectively). Percent moisture and percent crude fat in the semitendinosus were similar between treatments (P = 0.44, P = 0.42 respectively). Femur bone weight and length did not differ between treatments (P = 0.98 and P = 0.81 respectively). Muscle fiber diameter and area from the LM and semitendinosus were similar between treatment groups (P = 0.98, P = 0.98, P = 0.56, P = 0.64 respectively). Collectively these results suggest that fetal growth characteristics are not affected by maternal nutritional manipulation during mid-gestation in beef cows. However, differences in expression of fetal genes regulating adipose tissue growth and genes integral for myogenesis in the beef fetus could result in postnatal differences in postnatal composition and warrants further investigation.

Publisher

South Dakota State University

Comments

Cattle -- Fetuses -- Growth
Fetus -- Nuitrition

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In Copyright