Ruminantlarda yetersiz beslenmenin sindirimselve metabolik adaptasyonlar ve üreme üzerine etkileri

Yetersiz beslenme sonucu gözlenen kısa- (günlerce) ve orta-vadeli (haftalarca) adaptasyonlar daha çok iç organlar için söz konusudur. Diğer dokularda ise uzun-vadeli tepki kademeli bir mobilizasyonu kapsar (yağ>kas>kemik), fakat anatomik bölgeler açısından da bu sıralamada farklılıklar gözlenir. Yetersiz beslenen hayvanlarda, vücut lipidleri en yoğun olarak kullanılırken (%80'e kadar), protein kullanım oranı sınırlıdır (%15-20'ye kadar). Yetersiz beslenme esnasında enerji sarfiyatındaki azalma, çoğunlukla kısa- ve orta-vadede beslenme aktivetesindeki düşmeye ve iç organların kütle ve faaliyetindeki azalmaya bağlıdır. Uzun vadede ise, hem enerji sarfiyatı ve hem de doku kütleleri azalır, fakat her ünite doku ağırlığı başına sarfiyatta belirgin bir azalma olmaz. Azot kayıplarında gözlenen düşüşün nedenleri arasında da azot akışındaki azalma, böbreklerin azot atımını düşürmesi ve bazen de üre geri-dönüşümünün artması sayılabilir. Tüm bunlara rağmen, ruminantların yetersiz beslendiklerinde (yaşam payının altında) sindirim etkinliğini artırarak bu durumu telafi edemedikleri gözlenmektedir. Yetersiz beslenme durumlarında dokular arasında besin maddesi değişiminde pek çok hormon (insulin, büyüme hormonu, insulin-benzeri büyüme faktörü I, kateşolaminler, tiroit hormonları, kortizol, leptin, vs) rol oynar ve dokular arasındaki bu değişim, iç ortamın dengede tutulmasında (homeostazis) ve/veya hayvanın verim faaliyetlerinin devamlılığının sağlanmasında (teleoforez) önemli rol oynar. Bu da, ya çevresel dokularda sentez ve/veya yıkımlanmanın kontrolü (yağ doku ve kas) veya substratlann karaciğerde dönüşümleri (glukoneogenezis, ürogenezis ve ketogenezis) sayesinde sağlanır. Ayrıca, yetersiz beslenen hayvanlarda üreme süreci durabilir.

Digestive and metabolic adaptations of ruminants to undernutrition, and consequences on reproduction

In response to undernutrition, short- (days) and medium-term (weeks) adaptations are more pronounced for splanchnic organs than for other tissues. For the latter, the long-term response involves a sequential mobilization (fat>muscle>bone) with relative priorities differing among anatomical sites. Among chemical components, the body lipids are extensively used (up to 80 %) in underfed animals, while the range of protein utilization is limited (up to 15-20 %). The decrease in energy expenditure during undernutrition is mostly due to short- and medium-term decrease in feeding activity, and in the mass and activity of splanchnic tissues. In the long-term, energy expenditure and tissue masses decrease concomitantiy, but there does not appear to be a significant decrease in the expenditure per unit tissue weight. Nitrogen losses decrease in response to decline in nitrogen fluxes and also due to sparing by renal activities and sometimes by urea recycling. However, ruminants do not seem to be able to compensate for a low level of intake (below maintenance) by an increase in digestive efficiency. Numerous hormones (insulin, growth hormone, insulin-like growth factor I, catecholamines, thyroid hormones, cortisol, leptin, etc.) are involved in the changes during undernutrition of nutrient fluxes between tissues (adipose tissue and muscle), ör through hepatic conversions of substrates (gluconeogenesis, ureagenesis and ketogenesis), in order to maintain the constancy of the internal environment (homeostasis) and/or to sustain productive functions (teleophoresis). However, reproductive process may be blocked in underfed animals.

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