Forage fibre quality as a determinant of nitrogen use efficiency in dairy cows

Malherbe, Charl Stephen (2017-03)

Thesis (MSc)--Stellenbosch University, 2017.

Thesis

ENGLISH ABSTRACT: Pollution from dairy farming, in the form of nitrogen emissions, is becoming an increasing concern globally due to greenhouse gasses and global warming. Many countries around the world, especially in the European Union (EU), have already put in place regulations regarding treatment of dairy farm effluent in an attempt to reduce nitrogen emissions. Many studies are also focussing on possible ways in which nitrogen excretion from cows can be reduced. Although none of these regulations are currently in place in South Africa it is likely that they soon will be as our agricultural practices follow EU regulations closely. Four lactating Holstein cows were used in a 4 x 4 Latin square design balanced for carryover effects with a 2 x 2 factorial arrangement of treatment. Treatments were low crude protein (CP) concentration with high neutral detergent fibre (NDF) digestibility (LpHd), high CP concentration with high NDF digestibility (HpHd), low CP concentration with low NDF digestibility (LpLd) and high CP concentration with low NDF digestibility (HpLd). Crude protein concentrations for the rations were formulated to be around 18% for Hp and about 15% for Lp. The indigestible NDF, as % of the NDF, of the two oat hays used were 40.8% for Ld hay and 35.54% for the Hd hay. Wheat straw was included in the Ld diets to obtain iso-NDF diets of different quality. Cows were fed ad libitum for 14 days with data collection taking place over the last 4 days of each period. The aim of this study was to improve nitrogen use efficiency (NUE) and to investigate the possible economic benefits for dairy farmers presented through better nutritional management by optimizing the use of dietary protein by using better quality forages (with regard to the digestible NDF) and by reducing CP intake by formulating the diets to meet metabolisable protein (MP) requirements. Dry matter intake (DMI) and milk yields (MY) were recorded daily and DMI for 3 of the diets was found to be similar, with the exception of the LpLd diet (i.e. LpLd had lower DMI than the other 3 diets) showing how protein availability can counteract the lower forage quality, by stimulating fibrolytic bacteria. Energy corrected milk yield (ECM) was found to drop 2.46kg/d for Hd diets and 3.00kg/d for Ld diets with Hp having higher production then Lp levels. Nitrogen use efficiency was found to improve by 3.04% when protein was reduced in combination with Hd forages and by 5.63% for Ld forages. Dry matter intakes and milk yields were used to determine daily feed costs and income respectively. These were used to calculate income over feed cost (IOFC). It was seen the higher protein diets had a higher cost per day but also resulted in higher milk production. The impact of better quality forages can also clearly be seen, especially on the lower protein levels. Statistically diet had no effect on IOFC, with IOFC being the same across all treatments. We concluded that lowering protein improved NUE significantly with forage digestibility contributing to the level of improvement. However, a consequence of reducing CP was a corresponding decrease in production. Although no statistical difference was found for IOFC, numerical differences that would be considered significant on farm level were however observed. The lack of statistical significance is a possible consequence of high standard errors of the mean (SEM) resulting from limited data point and thus we recommend performing this study on a larger herd to improve statistical variation.

AFRIKAANS OPSOMMING: Besoedeling vanaf melkboerderye, in die vorm van stikstof uitskeiding word 'n toenemende kommer wêreldwyd as gevolg van kweekhuisgasse en aardverwarming. Baie lande wêreldwyd, veral in die Europese Unie (EU), het reeds wetgewing in plek gestel met betrekking tot die verwerking van melkkery storting in 'n poging om stikstof besoedeling te verminder. Vele studies is reeds onderneem om moontlike verlaging van stikstofbesoedeling te weeg te bring. In Suid-Afrika is daar tans geen regulasie ten opsigte van die storting van afvalstowwe nie. Dit sal egter na alle warskynlikheid die EU voorbeeld binnekort volg. Vier lakterende Holstein koeie is gebruik in 'n 4 x 4 Latynse vierkant ontwerp gebalanseer vir oordrag effekte met 'n 2 x 2 faktoriale behandeling. Behandelings was lae ruproteïen (RP) konsentrasie met 'n hoë neutraal bestande vesel (NBV) verteerbaarheid (LpHd), 'n hoë RP konsentrasie met 'n hoë NBV verteerbaarheid (HpHd), lae RP konsentrasie met 'n lae NBV verteerbaarheid (LpLd) en 'n hoë RP konsentrasie met 'n lae NBV verteerbaarheid (HpLd). Ruproteïen konsentrasies vir die rantsoene is geformuleer om ongeveer 18% te wees vir Hp en 15% vir Lp. Die onverteerbare NBV, as ‘n % van NBV, van die twee hawerhooi bronne wat gebruik was, is 40.8% vir Ld hooi en 35.54% vir die Hd hooi. Koringstrooi is ingesluit in die Ld dieet om gelyke-NBV diëte te kry met verskillende verteerbaarhede. Koeie is ad libitum gevoer vir 14 dae op elke dieet met data-kolleksie oor die laaste 4 dae van elke tydperk. Die doel van hierdie studie was om stikstofgebruiks-doeltreffendheid (SGD) te verbeter en om die moontlike ekonomiese voordele vir melkboere te ondersoek: eerstens, deur beter voedingswaardebestuur en die optimalisering van die gebruik van proteïen met behulp van beter verteerbare ruvoer (NBV) en tweedens, deur die vermindering van RP inname deur die diëte te formuler om metaboliseerbare proteïen (MP) vereistes te voldoen. Droëmateriaal inname (DMI) en melkproduksie (MP) is daagliks aangeteken en DMI vir 3 van die diëte was soortgelyk aan mekaar met die uitsondering van die LpLd dieet. Die LpLd het ‘n laer DMI as die ander 3 diëte gehad, wat daarop dui dat hoeproteïen beskikbaarheid die laer kwaliteid ruvoer teenwerk deur die stimulering van veselverteerende bakterieë. Energiegekorrigeerde melkproduksie (EGM) was 2.46kg / d laer vir Hd diëte en 3.00kg / d vir Ld diëte resepktiewelik met hoër melk produksie vir Hp diete teenoor Lp diëte. Die vermindering van proteïen in kombinasie met Hd en Ld ruvoer het stikstofgebruik-doeltreffendheid met 3.04% en met 5.63% onderskeidelik vermeerder. Droëmateriaal inname en melkproduksie is gebruik om daaglikse voerkoste en -inkomste te bepaal en om marge bo voerkoste (MBVK) te bereken. Hoër proteïen diëte het beide 'n hoër koste per dag gehad en ‘n hoër melkproduksie gehad. Die invloed van hoër kwaliteit ruvoer is duidelik, veral met die laer proteïen diëte. Geen statistiese verskille is met MBVK tussen behandelings waargeneem nie Ons gevolgtrekking was dat die verlaging van proteïen vlakke die SGD verbeter het en dat ruvoerverteerbaarheid ‘n beduidende bydrae gemaak het. Verlaagte RP het egter melkproduksie onderdruk. Hoewel geen statistiese verskil vir MBVK gevind is nie, was daar wel numeriese verskille wat op plaasvlak ‘n beduidende verskil sal maak. Weens ‘n gebrek aan ‘n groot genoeg datastel en die gevolglike hoë standard afwyking, is geen statistiese betekenisvolheid tussen behandelings waargeneem nie.

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