Wiersma is the alfalfa business manager with DuPont Pioneer. Thomas retired from the William H. Miner Agricultural Research Institute and is president of Oak Point Agronomics Ltd.Starch leads a storied life on the modern dairy farm. It begins in the cornfields where sunlight converts water and carbon dioxide to sugars, and these sugars are stored as starch in the grain. Cows, being ruminant animals, have the unique ability to use both cellulose (fiber) and starch (grain) as energy sources.
The challenge facing dairy farmers is how to maximize energy in the diet while at the same time minimizing starch or grain cost. To reduce starch costs, high starch digestibility is critical.
Inquiring minds want to know
The study of starch in corn and dairy diets is not new, but recent promotion of “floury” corn silage hybrids has created confusion in the market. What are the right questions to ask when faced with claims about higher starch digestibility from corn hybrids with “floury” starch-type kernels? Are claims being made which, in fact, try to solve a problem that doesn’t exist?
What is the difference between corn kernels with floury versus hard starch?
When seed companies talk about hybrids with floury starch (also called soft or dent hybrids), they are referring to the amount of white-colored starch granules found in the corn kernel. Vitreous starch (also called hard or flinty) is the higher density, yellowish-colored starch granules found on the outer edges of a mature kernel. Vitreous starch becomes more prominent as kernels dry to moisture levels below 20 to 25 percent (postblack layer).
In both floury and vitreous corn kernels, starch granules are surrounded by proteins (prolamin or zein). The vitreous areas have more zein proteins and exhibit a much stronger bonding of starch by these zein proteins. One example of a corn hybrid with high vitreousness is popcorn. Also, many northern European corn hybrids are of the flinty type with more vitreous starch. Most North American corn hybrids are bred using dent genetics with higher floury starch content.
Where is starch digested in the cow?
Many claims about higher starch digestibility hybrids emphasize the importance of driving rumen bacterial populations. While important, ruminal digestion rates are only part of the equation. Starch digestibility hinges more on the answers to these questions: How much starch gets digested in the total digestive tract (rumen + small intestine + large intestine), and how much is associated with seed genetics versus kernel processing and storage management?
Total tract digestion can easily be determined by measuring starch in the feces. Research literature and lab summaries indicate that total tract starch digestion in lactating cattle exceeds 95 percent when proper kernel processing in silage, high-moisture corn, or dry grain is achieved.
Nutritionists routinely measure fecal starch of less than 2 to 3 percent in well-managed herds. If 98 to 99 percent of the starch has been digested by the time the corn silage and grain leave the animal, it raises the question: What problem are we trying to solve?
While total tract digestion is most important, it is helpful to understand the balancing act of where starch is digested in the animal. Starch digestion in the rumen is beneficial for growing more rumen bugs that provide a protein source for the cow.
However, too much starch digested in the rumen can cause acidosis and cows might go off-feed and have low milk components. Rumen bypass starch, absorbed as glucose from the intestines, can have more than 20 percent greater caloric value to the animal compared with starch fermented in the rumen.
Do corn genetics differ in starch digestibility?
University studies have shown minimal differences in the amount of floury starch among dent hybrids when kernels are greater than 25 percent moisture (typical moisture for corn silage or high-moisture corn).
Vitreousness differences may occur among hybrids when harvested at kernel moisture less than 20 to 25 percent. Even these differences may be small and will vary from year-to-year based on growing conditions.
What can be done to improve starch digestibility?
Researchers have shown that the primary drivers of high starch digestibility of corn silage, high-moisture corn, or dry grain includes the following.
- Kernel particle size — influenced most by kernel processing or grinding.
- Duration of time in fermented storage — starch digestibility increases in the silo for about six months before stabilizing.
- Kernel maturity or moisture at harvest (one-half milkline versus black layer) — impacts the extent of vitreous starch development.
- The corn growing environment, including weather-related factors and nitrogen fertilization.
The largest single factor in managing corn starch digestibility starts in the field at harvest time by frequently monitoring kernel particle size as the crop is being put into storage. Despite a trend to market “floury” starch corn hybrids, it is still in your best interest to focus genetic choices on yield and agronomics.
Wiersma ni meneja wa biashara ya alfalfa na DuPont Pioneer. Thomas ni mkurugenzi wa William H. Miner Agricultural Research Institute na ni mwenyekiti wa Oak Point Agronomics Ltd. Katika mashamba ya mahindi, jua hubadilisha maji na kaboni dioksidi kuwa sukari, ambayo huhifadhiwa kama wanga. Ng'ombe, wakiwa wanyama wa kutafuna, wana uwezo wa kipekee wa kutumia cellulose (fiber) na starch ( nafaka) kama vyanzo vya nishati. Msaada wa wakulima wa maziwa ni kuongeza nishati katika chakula na wakati huo huo kupunguza gharama ya wanga au nafaka. Ili kupunguza gharama za wanga, ni muhimu kuwa na wanga wenye uwezo mkubwa wa kumeng'enywa. Utafiti wa wanga katika chakula cha mahindi na maziwa si mpya, lakini kukuza hivi karibuni kwa mahindi ya "floury" ya mahindi ya mahindi imesababisha machafuko sokoni. Ni maswali gani sahihi ya kuuliza wakati kukabiliwa na madai kuhusu juu ya starch digestibility kutoka mahindi hybrids na <unk>floury<unk> starch-aina ya kernels? Je, madai yanayotolewa ambayo, kwa kweli, yanajaribu kutatua tatizo ambalo halipo? Ni nini tofauti kati ya mahindi yenye unga na mahindi yenye wanga mgumu? Kampuni za mbegu zinapozungumzia mbegu zenye unga na wanga (zilizojulikana pia kama mbegu laini au za mviringo), zinaonyesha kiasi cha chembe za unga zenye rangi nyeupe zilizopatikana katika mahindi. Vitreous starch (pia inaitwa ngumu au flinty) ni juu ya wiani, manjano-rangi starch granules kupatikana juu ya kingo za nje ya kernel kukomaa. Vitriol ya vitriol inakuwa na nguvu zaidi wakati nyuzinyuzi zinapokauka hadi kiwango cha unyevu chini ya asilimia 20 hadi 25 (safu ya baada ya nyeusi). Katika mahindi ya mahindi yenye unga na ya kioo, chembe za starch huzungukwa na protini (prolamin au zein). Maeneo ya vitreous yana protini zaidi za zein na yanaonyesha uhusiano mkubwa zaidi wa wanga na protini hizi za zein. Mfano mmoja wa mchanganyiko wa mahindi wenye rangi ya kioo ni popcorn. Pia, mahindi mengi ya kaskazini mwa Ulaya ni ya aina ya flinty yenye wanga mwingi wa kioo. Mimea mingi ya mahindi ya Amerika Kaskazini huzawa kwa kutumia chembe za urithi za dent zenye kiasi cha juu cha wanga. Nyama ya ng'ombe huhisije chachu? Madai mengi kuhusu mimea ya mchanganyiko yenye nguvu zaidi ya kumeng'enya inasisitiza umuhimu wa kuendesha idadi ya bakteria za rumen. Ingawa ni muhimu, viwango vya kumeng'enya chakula kwa wanyama wa mnyama ni sehemu tu ya usawa huo. Uwezo wa kumeng'enya ni muhimu kwa sababu ya jinsi ya kuunganisha na kuhifadhiwa kwa starch katika mfumo wa utumbo (Rumen, Small intestine, na colon) na jinsi ya kuunganisha na utamaduni wa mbegu. Upasuaji wa jumla wa njia ya kumeng'enya unaweza kuamuliwa kwa urahisi kwa kupima wanga katika matumbo. Uchunguzi na muhtasari wa fasihi ya maabara unaonyesha kwamba jumla ya digestive ya wanga katika ng'ombe wa kunyonyesha inazidi 95%, wakati usindikaji sahihi wa kernel katika silage, mahindi yenye unyevu wa juu, au nafaka kavu inapatikana. Wataalamu wa lishe hupima kwa kawaida kiwango cha wanga wa matope chini ya asilimia 2 hadi 3 katika mifugo inayosimamiwa vizuri. "Ikiwa asilimia 98 hadi 99 ya wanga umemeng'enywa wakati mbegu za mahindi zinapoondoka kwenye mnyama, hilo linaibua swali: ""Tunajaribu kutatua tatizo gani?""" Ingawa digestive mfumo wa jumla ni muhimu zaidi, ni muhimu kuelewa hatua ya kusawazisha ambapo starch ni digested katika mnyama. Upasuaji wa wanga katika tumbo la ng'ombe ni muhimu kwa kukuza wadudu wengi wa tumbo la ng'ombe ambao hutoa chanzo cha protini kwa ng'ombe. Hata hivyo, wanga mwingi sana unaotawanywa katika tumbo la tumbo la tumbo la tumbo la tumbo la tumbo la tumbo la tumbo la tumbo la tumbo la tumbo la tumbo la tumbo la tumbo la tumbo la tumbo la tumbo la tumbo la tumbo la tumbo. Rumen bypass starch, ambayo huingizwa kama glukosi kutoka matumbo, inaweza kuwa na thamani ya kalori zaidi ya asilimia 20 kwa mnyama ikilinganishwa na starch iliyopandwa katika rumen. Je, mbegu za mahindi hutofautiana katika uwezo wa kumeng'enya wanga? Uchunguzi wa chuo kikuu umeonyesha tofauti ndogo katika kiasi cha starch ya unga kati ya dent hybrids wakati kernels ni zaidi ya 25% unyevu (unyevu wa kawaida kwa mahindi ya mahindi au mahindi ya unyevu wa juu). Tofauti za vitreousness zinaweza kutokea kati ya mseto wakati wa kuvuna kwa unyevu wa kernel chini ya asilimia 20 hadi 25. Hata tofauti hizi zinaweza kuwa ndogo na zitatofautiana kutoka mwaka hadi mwaka kulingana na hali za kukua. Ni nini kinachoweza kufanywa ili kuboresha utambuzi wa wanga? Watafiti wameonyesha kwamba madereva ya msingi ya digestibility ya juu ya starch ya mahindi silage, high-unyevu mahindi, au nafaka kavu ni pamoja na yafuatayo: - ukubwa wa chembechembe kernel <unk> kuathiriwa zaidi na kernel usindikaji au kusaga. - Muda wa kuhifadhiwa katika fermented <unk> starch digestibility huongezeka katika silo kwa takriban miezi sita kabla ya utulivu. - Kernel ukomavu au unyevu wakati wa mavuno (nusu milkline dhidi ya safu nyeusi) <unk> athari kiasi cha vitreous starch maendeleo. - Mazingira ya kukua mahindi, ikiwa ni pamoja na mambo yanayohusiana na hali ya hewa na mbolea ya nitrojeni. Sababu kubwa ya kuendesha digestibility ya starch ya mahindi huanza katika shamba wakati wa mavuno kwa mara kwa mara kufuatilia ukubwa wa chembe za kernel wakati mazao yanawekwa kwenye kuhifadhi. Licha ya mwelekeo wa soko <unk>floury<unk> starch mahindi hybrids, bado ni katika maslahi yako bora kuzingatia uchaguzi wa maumbile juu ya mavuno na agronomics.