Assoumaya, Caroline (2007) Study of limiting factors of intake in small ruminants fed with tropical forages. PhD thesis Animale, INRA, UR143 Zootechnie,, AgroParistech 2007AGPT0022 p.304.

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Abstract

The aim of this study was to analyse the relative impact of physical, biological and biochemical phenomena on intake and digestion of tropical forages. The hypothesis of this study were : 1) intake and digestibility of tropical forages could be improved if valorized at a younger age, 2) cellulolytic potential of the rumen would not be the first limiting factor of intake and digestion of forages, 3) reduction rate of size of diet by chewing (comminution), would be the first limiting factor of intake. In a first time, a meta-analysis of the data of the literature has been conducted. In a second time, 2 groups of trials have been realized to: 1) define the experimental conditions of the second group; 2) validate the hypothesis.

Results of the meta-analysis have confirmed that intake of temperate forage was significantly higher than tropical forage (68.70 vs 57.83 g/MW; P<0.001). Moreover, the meta-analysis has underscored that chewing work of 1kg of DM of tropical forage was twice more important than with temperate forage.

Results of the first experimental group have proved: 1) the efficacy of addition of a fibrolytic exogeneous enzyme (degradability after 24h of a 56-day-old chopped forage : 32.14 vs 39.25% without and with enzyme respectively; P<0.0001); 2) that ingestive and digestive parameters vary with frequency of the meal (whole rumen content of a 21-day-old forage: 1.01 vs 0.77 g/gDMI with 4 and 2 meals respectively; P<0.001); 3) that ingestive and digestive parameters were function of the nycthemeral period (chewing index of a 56-day-old grass was 1.07 vs 1.52 during the diurnal and nocturnal period respectively; P<0.05). Study of the digestive dynamics has been conducted during the second experimental group with two meals per day, measures have been realized on the 24h- period. Study realized in non limiting enzymatic condition has been set up with addition of the exogeneous fibrolytic enzyme.

Results of the second experimental group have underscored that 1) intake and digestibility significantly decreased with maturity of the forage (DMI was 86.69, 83.10, 69.37, 59.29 and 50.60 g/MW for the 14-, 21-, 28-, 42- and 56-day-old grass respectively; P<0.02); 2) intake did not vary with the cellulolytic activity (P>0.4); 3) intake was negatively related with the chewing index (DMI (g/MW) = 125 – 65.3 ChewId; P<0.03).

In conclusion, tropical young forages (<28 days) present good nutritive value. Besides, cellulolytic potential would not be the first limiting factor of intake but rather the comminution rate. The important impact of the individual variability on intake, registered during experimentations of the thesis, have to be confirmed.

Table of content

Liste des abréviations – Glossaire 7

INTRODUCTION GENERALE 11

ETUDE BIBLIOGRAPHIQUE 17

PUBLICATION 1. : Etude comparative de l’ingestion et de la digestion des fourrages

tropicaux et tempérés 19

PARTIE EXPERIMENTALE 50

PUBLICATION 2. : Limits of exogenous fibrolytic enzymes to improve digestion and intake

of a tropical grass 56

PUBLICATION 3. : Effect of frequency of meals on intake and digestion of tropical grass

consumed by rams 73

PUBLICATION 4. : Feeding behaviour and rumen load in related sheep receiving two equal

meal of a tropical forage 102

PUBLICATION 5. : Intake and digestive processes in the rumen of rams fed with Digitaria

decumbens harvested at four stages of grass regrowth age 129

PUBLICATION 6. : Intake and digestive processes of rams fed Panicum maximum

harvested at four stages of grass maturity 146

PUBLICATION 7. : Rumen fermentation in rams fed Panicum maximum harvested at four

stages of grass maturity 167

PUBLICATION 8. : Intake and digestive processes of rams fed Digitaria decumbens

harvested at three stages of grass maturity 192

DISCUSSION GENERALE -CONCLUSIONS 221

LISTE DES FIGURES ET TABLEAUX 251

REFERENCES BIBLIOGRAPHIQUES 263

FORMATIONS SUIVIES 302

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